Details of a Researcher - NISHIMURA Yasuhiro

Papers - NISHIMURA Yasuhiro

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Impact of external radiation on dark rate noise measurement for the Hyper-Kamiokande photomultiplier tube

Mandokoro Y., Bronner C., Ishitsuka M., Tashiro T., Nishimura Y.

Journal of Instrumentation 20 ( 5 ) 2025.05

The Hyper-Kamiokande (HK) is a next-generation water Cherenkov detector currently under construction in Japan as of 2025, and scheduled to begin operation in 2027. A new PMT has been developed for HK with improvements in detection efficiency, timing resolution, and pressure tolerance by a factor of two with respect to those used in the Super-Kamiokande detector. The HK detector will be instrumented with 20,000 photomultiplier tubes (PMT). Currently, the PMTs are produced, and the performance testing of the delivered PMTs is underway in parallel. In this test, it was observed that the dark rate values differed depending on the measurement location. The difference is considered due to environmental radiation, and we have conducted measurements of dark rate variations with radiation sources. We measured correlations between the irradiation of γ rays and dark noise rate and the evaluated intrinsic dark noise rate of HK PMT after subtracting the contribution due to environmental radiation.

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Optimization of geomagnetic shielding based on detection efficiency

Cabo S.R., Nishimura Y., Gómez S.L.S., Bonavera L., Sanchez M.L., Santos J.D., de Cos F.J.

European Physical Journal Plus 140 ( 4 ) 2025.04

Due to the progressive increase in size of the latest Cherenkov-type detectors, it is becoming increasingly important to design a suitable compensation system based on coils of the Earth’s magnetic field to ensure the correct operation of the photomultipliers (PMTs). Until now, most studies have assessed the correct functioning of such a system by the proportion of PMTs experiencing more than 100 mG of magnetic field perpendicular to their axis. In the present study, we discuss whether this evaluation parameter is the most appropriate and propose the average residual perpendicular magnetic field <Bperp> as an alternative that more closely reflects the loss of detection efficiency of PMTs. A compensation system design is also proposed that offers good results as well as being economical to optimize this parameter.

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First Joint Oscillation Analysis of Super-Kamiokande Atmospheric and T2K Accelerator Neutrino Data

Abe K., Abe S., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Mirabito J., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Rogly R., Nakamura T., Jang J.S., MacHado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Feltre M., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Périssé L., Pronost G., Fujisawa C., Horiuchi S., Kobayashi M.

Physical Review Letters 134 ( 1 ) 2025.01

ISSN 00319007

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7(16.3)×1020 protons on target in (anti)neutrino mode, the analysis finds a 1.9σ exclusion of CP conservation (defined as JCP=0) and a 1.2σ exclusion of the inverted mass ordering.

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Search for proton decay via p →e+η and p →μ+η with a 0.37 Mton-year exposure of Super-Kamiokande

Taniuchi N., Abe K., Abe S., Asaoka Y., Bronner C., Harada M., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakayama S., Noguchi Y., Pronost G., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Mirabito J., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Kim J.Y., Lee S.H., Lim I.T., Moon D.H., Park R.G., Yang B.S., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Rogly R., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G.

Physical Review D 110 ( 11 ) 2024.12

ISSN 24700010

A search for proton decay into e+/μ+ and a η meson has been performed using data from a 0.373 Mton·year exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear η interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and ∼10% increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of 1.4×1034 years for p→e+η and 7.3×1033 years for p→μ+η at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date.

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Measurements of the charge ratio and polarization of cosmic-ray muons with the Super-Kamiokande detector

Kitagawa H., Tada T., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Kearns E., Raaf J.L., Wan L., Wester T., Pointon B.W., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Paganini P., Quilain B., Rogly R., Santos A.D., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Marin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L.

Physical Review D 110 ( 8 ) 2024.10

ISSN 24700010

We present the results of the charge ratio (R) and polarization (P0μ) measurements using decay electron events collected between September 2008 and June 2022 with the Super-Kamiokande detector. Because of its underground location and long operation, we are able to perform high-precision measurements by accumulating cosmic-ray muons. We measured the muon charge ratio to be R=1.32±0.02(stat+syst) at EμcosθZenith=0.7-0.2+0.3 TeV, where Eμ is the muon energy and θZenith is the zenith angle of incoming cosmic-ray muons. This result is consistent with the Honda flux model while indicating a tension with the πK model of 1.9σ. We also measured the muon polarization at the production location to be P0μ=0.52±0.02 (stat+syst) at the muon momentum of 0.9-0.1+0.6 TeV/c at the surface of the mountain; this also suggests a tension with the Honda flux model of 1.5σ. This is the most precise measurement ever to experimentally determine the cosmic-ray muon polarization near 1 TeV/c. These measurement results are useful to improve atmospheric neutrino simulations.

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Combined Pre-supernova Alert System with KamLAND and Super-Kamiokande

Abe S., Eizuka M., Futagi S., Gando A., Gando Y., Goto S., Hachiya T., Hata K., Ichimura K., Ieki S., Ikeda H., Inoue K., Ishidoshiro K., Kamei Y., Kawada N., Kishimoto Y., Koga M., Kurasawa M., Mitsui T., Miyake H., Morita D., Nakahata T., Nakajima R., Nakamura K., Nakamura R., Nakane J., Ozaki H., Saito K., Sakai T., Shimizu I., Shirai J., Shiraishi K., Shoji R., Suzuki A., Takeuchi A., Tamae K., Watanabe H., Watanabe K., Yoshida S., Umehara S., Fushimi K., Kotera K., Urano Y., Berger B.E., Fujikawa B.K., Learned J.G., Maricic J., Fu Z., Smolsky J., Winslow L.A., Efremenko Y., Karwowski H.J., Markoff D.M., Tornow W., Dell’Oro S., O’Donnell T., Detwiler J.A., Enomoto S., Decowski M.P., Weerman K.M., Grant C., Song H., Li A., Axani S.N., Garcia M., Suzuki S., Abe K., Abe S., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S.

Astrophysical Journal 973 ( 2 ) 2024.10

ISSN 0004637X

Preceding a core-collapse supernova (CCSN), various processes produce an increasing amount of neutrinos of all flavors characterized by mounting energies from the interior of massive stars. Among them, the electron antineutrinos are potentially detectable by terrestrial neutrino experiments such as KamLAND and Super-Kamiokande (SK) via inverse beta decay interactions. Once these pre-supernova (pre-SN) neutrinos are observed, an early warning of the upcoming CCSN can be provided. In light of this, KamLAND and SK, both located in the Kamioka mine in Japan, have been monitoring pre-SN neutrinos since 2015 and 2021, respectively. Recently, we performed a joint study between KamLAND and SK on pre-SN neutrino detection. A pre-SN alert system combining the KamLAND detector and the SK detector was developed and put into operation, which can provide a supernova alert to the astrophysics community. Fully leveraging the complementary properties of these two detectors, the combined alert is expected to resolve a pre-SN neutrino signal from a 15 M <inf>⊙</inf> star within 510 pc of the Earth at a significance level corresponding to a false alarm rate of no more than 1 per century. For a Betelgeuse-like model with optimistic parameters, it can provide early warnings up to 12 hr in advance.

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Development of a Data Overflow Protection System for Super-Kamiokande to Maximize Data from Nearby Supernovae

Mori M., Abe K., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Rogly R., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L., Gonin M., Perisse L.

Progress of Theoretical and Experimental Physics 2024 ( 10 ) 2024.10

Neutrinos from very nearby supernovae, such as Betelgeuse, are expected to generate more than ten million events over 10 s in Super-Kamokande (SK). At such large event rates, the buffers of the SK analog-to-digital conversion board (QBEE) will overflow, causing random loss of data that are critical for understanding the dynamics of the supernova explosion mechanism. In order to solve this problem, two new data-acquisition (DAQ) modules were developed to aid in the observation of very nearby supernovae. The first of these, the SN module, is designed to save only the number of hit photomultiplier tubes during a supernova burst and the second, the Veto module, prescales the high-rate neutrino events to prevent the QBEE from overflowing based on information from the SN module. In the event of a very nearby supernova, these modules allow SK to reconstruct the time evolution of the neutrino event rate from beginning to end using both QBEE and SN module data. This paper presents the development and testing of these modules together with an analysis of supernova-like data generated with a flashing laser diode. We demonstrate that the Veto module successfully prevents DAQ overflows for Betelgeuse-like supernovae as well as the long-term stability of the new modules. During normal running the Veto module is found to issue DAQ vetos a few times per month resulting in a total dead-time less than 1 ms, and does not influence ordinary operations. Additionally, using simulation data we find that supernovae closer than 800 pc will trigger the Veto module, resulting in a prescaling of the observed neutrino data.

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Evaluation of neutron tagging efficiency on 0.03% Gd mass concentration in SK-Gd experiment

Nakanishi F., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

Super-Kamiokande (SK) experiment started the "SK-Gd experiment" by dissolving gadolinium (Gd) sulfate octa-hydrate in ultra-pure water from the tank in July 2020. The neutron tagging efficiency has been improved compared to the pure-water phase by detecting a total energy of 8 MeV gamma rays emitted by thermal neutron capture on Gd. It enables us to improve, for example, the sensitivity of diffuse supernova neutrino background, the accuracy of the reconstruction for the supernova direction, and so on. For these physics targets, accurate evaluation of neutron identification efficiency is essential. In this presentation, I report the calibration results using an Am/Be neutron source to evaluate the efficiency at a Gd mass concentration of 0.03%, starting from June 2022, and the comparison of the estimated neutron detection efficiency with simulation.

Time-dependent and Time-independent Directional Search for High-Energy Astrophysical Neutrino Point Sources in Super-Kamiokande

Wang X., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

This contribution reports the results of the searches for high-energy astrophysical neutrino point sources in the energy range above GeV using Super-Kamiokande data. The searches include time-integrated and time-dependent full sky searches for both ν<inf>μ</inf> and ν<inf>e</inf> sources and coincidence check with candidates including TXS 0506+056 and NGC 1068. The searches use unbinned maximum likelihood method, and test statistics is calculated to find signal excess over atmospheric neutrino background. The time-integrated search method is updated from a previous search by adding the neutrino energy distribution in the likelihood to consider different power-law emission spectra with varying spectral indices. This is the first time to perform the time-dependent search, which has a better performance in searching for neutrino emission in a short time period, in Super-Kamiokande. Upper limits on neutrino flux or fluence are set for all searches.

Study of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos in the SK-Gd experiment

Sakai S., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

The atmospheric neutrino-oxygen neutral-current quasielasatic (NCQE) reactions are one of the main background in the search for supernova relic neutrinos. Here, we report the first measurement of the atmospheric neutrino-oxygen NCQE cross section in the Super-Kamiokande Gadolinium (SK-Gd) experiment using 552.2 days of full SK-VI data. The measured NCQE cross section is 0.74 ± 0.22(stat.) +<inf>−</inf>0.86<inf>0.16</inf>(syst.) × 10−38 cm2, which is consistent with the theoretical NCQE cross section and the previous study in SK within the range of the uncertainty. Furthermore, we established the verification method for nucleon-nucleus interaction models using atmospheric neutrino events. We performed the verification using the Bertini Cascade model (BERT), the Binary Cascade model (BIC) and the Liège Intranuclear Cascade model (INCL++). As a result, we suggested that BIC and INCL++ are closer to the observed data.

Status and Prospect of SK-Gd Project

Hino Y., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

In 2020, a new phase of Super-Kamiokande experiment, SK-Gd, was started by loading gadolinium into the pure water. This led to a high neutron detection efficiency, which allows us to distinguish different neutrino reactions, enhance signals and remove backgrounds more efficiently. In the summer of 2022, an update of SK-Gd was done by adding additional Gd, and thus totally 39 tonnes of gadolinium sulfate octahydrate has been introduced in the water. The Gd concentration was estimated as 0.0332±0.0002% based on the dissolved weight of gadolinium sulfate octahydrate powder. It is consistent with the result of the direct sampling from the detector as 334 ± 4 ppm. The spallation neutron measurement and AmBe calibration confirms the shorter capture time constant and higher capture event rate due to the second loading. Therefore, we achieved 1.5 times higher than that of the first loaded phase as expected.

Search for Boosted Dark Matter in Super-Kamiokande with low-energy electrons

Iovine N., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchene A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

Despite efforts from numerous experiments to grasp the nature of dark matter, no convincing dark matter signal has been observed so far and the very properties of this invisible matter remain unknown. Nevertheless, strong constraints on these properties are set by current observations, particularly for GeV to TeV WIMP-like dark matter particles. In contrast, sub-GeV dark matter scenarios are largely unexplored and still offer promising prospects for dark matter detection. In this contribution, we conduct a search for low-energy electrons scattered by boosted dark matter particles in the Super-Kamiokande detector. In particular, a two-component dark matter scenario is considered, which results in a natural boosting of the non-secluded secondary dark matter particles produced by the decay or annihilation of the dominant cold dark matter component. This work focuses on boosted dark matter from the centre of our Galaxy, with scattered electron energies ranging from a few MeV to a few hundred of MeV. We present the first sensitivities of such low-energy boosted dark matter search using Super-Kamiokande.

Measurement of the kaon to pion production ratio with the Super-Kamiokande

Tada T., Nakano Y., Koshio Y., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R.

Proceedings of Science 444 2024.09

Cosmic-ray muons are generated from the decay of mesons which are secondary particles produced via hadronic interaction between primary cosmic-ray particles and atmospheric nuclei at the upper the atmosphere. The mesons such pions and kaons mostly decay into muons immediately, reflecting the details of the hadronic interactions depending on their energy and lifetime. The modulation of the cosmic-ray muon rate as well as the flux and the atmospheric kaon-to-pion production ratio are important to determine the flux and energy of the atmospheric neutrino. In particular, the kaon-to-pion production ratio r<inf>K/π</inf> is measured with the correlation coefficient α<inf>T</inf> between the cosmic-ray muon rate in the underground detector and the atmospheric temperature. As a result, we obtained the correlation coefficient r<inf>K/π</inf> = 0.85 ± 0.01 (statistical uncertainty only) and r<inf>K/π</inf> = 0.12 ± 0.03 (statistical uncertainty only) using the data taken in 10 years at the Super-Kamiokande detector. In this article, we report the current status of measurement of the modulation of the comic-ray muon and the atmospheric kaon-to-pion production ratio.

Measurement of the charge ratio and polarization of cosmic-ray muon using the tagged decay-e events in Super-Kamiokande

Nakano Y., Tada T., Kitagawa H., Koshio Y., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y.

Proceedings of Science 444 2024.09

Neutrinos and muons from cosmic-ray interactions in the atmosphere originate from mesons, such as pions and kaons, in air-showers. An accuracy of the absolute atmospheric neutrino flux and its flavor ratio are limited due to the uncertainty of meson productions in hadronic interaction models. In order to reduce such uncertainty, measurements of the charge ratio and the polarization of cosmic-ray muons are important as new inputs to theoretical models which simulate the atmospheric neutrino flux. In this proceedings, we present the results of the charge ratio (R) and polarization (Pμ<inf>0</inf>) of cosmic-ray muon measurements using the decay electrons collected from 2008 September to 2022 June by the Super-Kamiokande (SK) detector. We measured muon charge ratio to be R = 1.32±0.02 (stat.+syst.) and the muon polarization at the production location to be Pμ<inf>0</inf> = 0.52±0.01 (stat.+syst.). The SK detector uniquely measured the polarization of cosmic-ray muons with energies more than 1 TeV at sea-level because of its underground location.

Measurement of cosmogenic 9Li in Super-Kamiokande with gadolinium loaded water

Shinoki M., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

Super-Kamiokande is a large water Cherenkov detector located approximately 1,000 m underground in Kamioka, Japan. The detector is a cylindrical tank 39.3 m in diameter and 41.4 m high, filled with about 50 kton of gadolinium loaded water. We measured 9Li isotopic nuclei produced by muon spallation using the data taken from 2020 to 2022 by the Super-Kamiokande detector with 0.011% gadolinium concentration in water. Cosmic-ray muons that penetrate the detector form hadron showers in water and secondary hadrons produce unstable radioisotopes through the spallation. Among those spallation products, 9Li is a long-lived radioactive isotope with a lifetime of about 0.26 seconds. It emits an electron and a neutron at a branching ratio of 50.8%, which is difficult to distinguish from the inverse beta decay caused by electron antineutrinos. Therefore, 9Li is one of the main background sources in the observation of diffuse supernova neutrino background. In this study, the energy spectrum of the electrons was measured with a threshold at 4.5 MeV which is lowered from the previous result with pure water. We will report the analysis method and results.

First result of a search for Diffuse Supernova Neutrino Background in SK-Gd experiment

Harada M., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Proceedings of Science 444 2024.09

Since 2020, Super-Kamiokande (SK) detector has been updated by loading gadolinium (Gd) as a new experimental phase, ‘SK-Gd.’ In the SK-Gd experiment, we can search low-energy electron antineutrinos via inverse-beta decay with efficient neutron identification thanks to high cross-section and high-energy gamma-ray emission of thermal neutron capture on Gd. Until July 2022, the observation is operated with the 0.01% Gd mass concentration. The neutron capture fraction on Gd is about 50% in this situation. In this paper, the first search result for the flux of astrophysical electron antineutrinos for the energy range of O(10) MeV in SK-Gd with a 22.5 × 552 kton·day exposure at 0.01% Gd mass concentration of the initial stage of SK-Gd is reported.

New methods and simulations for cosmogenic induced spallation removal in Super-Kamiokande-IV

Locke S., Coffani A., Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Yano T., Hirade K., Kanemura Y., Miki S., Watabe S., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Wang X., Megias G.D., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Yankelevich A., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Drapier O., Hedri S.E., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Santos A.D., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Sztuc A.A., Uchida Y., Martin D., Scott M., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Mattiazzi M., Ludovici L., Nishimura Y., Maewaka Y., Cao S.

Physical Review D ( 3 ) 2024.08

ISSN 24700010

Radioactivity induced by cosmic muon spallation is a dominant source of backgrounds for O(10 MeV) neutrino interactions in water Cherenkov detectors. In particular, it is crucial to reduce backgrounds to measure the solar neutrino spectrum and find neutrino interactions from distant supernovae. In this paper we introduce new techniques to locate muon-induced hadronic showers and efficiently reject spallation backgrounds. Applying these techniques to the solar neutrino analysis with an exposure of 2790×22.5 kton·day increases the signal efficiency by 12.6%, approximately corresponding to an additional year of detector running. Furthermore, we present the first spallation simulation at Super-Kamiokande, where we model hadronic interactions using fluka. The agreement between the isotope yields and shower pattern in this simulation and in the data gives confidence in the accuracy of this simulation, and thus opens the door to use it to optimize muon spallation removal in new data with gadolinium-enhanced neutron capture detection.

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Second gadolinium loading to Super-Kamiokande

Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Rogly R., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Périssé L., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 1065 2024.08

ISSN 01689002

The first loading of gadolinium (Gd) into Super-Kamiokande in 2020 was successful, and the neutron capture efficiency on Gd reached 50%. To further increase the Gd neutron capture efficiency to 75%, 26.1 tons of Gd<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>⋅8H<inf>2</inf>O was additionally loaded into Super-Kamiokande (SK) from May 31 to July 4, 2022. As the amount of loaded Gd<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>⋅8H<inf>2</inf>O was doubled compared to the first loading, the capacity of the powder dissolving system was doubled. We also developed new batches of gadolinium sulfate with even further reduced radioactive impurities. In addition, a more efficient screening method was devised and implemented to evaluate these new batches of Gd<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>⋅8H<inf>2</inf>O. Following the second loading, the Gd concentration in SK was measured to be 333.5±2.5 ppm via an Atomic Absorption Spectrometer (AAS). From the mean neutron capture time constant of neutrons from an Am/Be calibration source, the Gd concentration was independently measured to be 332.7 ± 6.8(sys.) ± 1.1(stat.) ppm, consistent with the AAS result. Furthermore, during the loading the Gd concentration was monitored continually using the capture time constant of each spallation neutron produced by cosmic-ray muons, and the final neutron capture efficiency was shown to become 1.5 times higher than that of the first loaded phase, as expected.

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Performance of SK-Gd’s Upgraded Real-time Supernova Monitoring System

Kashiwagi Y., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Rogly R., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Périssé L., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R.

Astrophysical Journal 970 ( 1 ) 2024.07

ISSN 0004637X

Among multimessenger observations of the next Galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. In 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd’s real-time supernova monitoring system has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on 2021 December 13, and is available through GCN Notices. When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd’s response to a simulated Galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd’s pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3° to 7° depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view.

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Search for Periodic Time Variations of the Solar B 8 Neutrino Flux between 1996 and 2018 in Super-Kamiokande

Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Jang M.C., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., MacHado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M.

Physical Review Letters 132 ( 24 ) 2024.06

ISSN 00319007

We report a search for time variations of the solar B8 neutrino flux using 5804 live days of Super-Kamiokande data collected between May 31, 1996, and May 30, 2018. Super-Kamiokande measured the precise time of each solar neutrino interaction over 22 calendar years to search for solar neutrino flux modulations with unprecedented precision. Periodic modulations are searched for in a dataset comprising five-day interval solar neutrino flux measurements with a maximum likelihood method. We also applied the Lomb-Scargle method to this dataset to compare it with previous reports. The only significant modulation found is due to the elliptic orbit of the Earth around the Sun. The observed modulation is consistent with astronomical data: we measured an eccentricity of (1.53±0.35)%, and a perihelion shift of (-1.5±13.5) days.

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Solar neutrino measurements using the full data period of Super-Kamiokande-IV

Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Imaizumi S., Iyogi K., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Kato Y., Kishimoto Y., Miki S., Mine S., Miura M., Mochizuki T., Moriyama S., Nagao Y., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Okada T., Okamoto K., Orii A., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang R., Wang X., Yoshida S., Bravo-Berguño D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Blaszczyk F.D.M., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Yankelevich A., Ganezer K.S., Hill J., Jang M.C., Kim J.Y., Lee S., Lim I.T., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Imber J., Mueller T.A., Paganini P., Rogly R., Quilain B., Santos A., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Matsuno S.

Physical Review D 109 ( 9 ) 2024.05

ISSN 24700010

An analysis of solar neutrino data from the fourth phase of Super-Kamiokande (SK-IV) from October 2008 to May 2018 is performed and the results are presented. The observation time of the dataset of SK-IV corresponds to 2970 days and the total live time for all four phases is 5805 days. For more precise solar neutrino measurements, several improvements are applied in this analysis: lowering the data acquisition threshold in May 2015, further reduction of the spallation background using neutron clustering events, precise energy reconstruction considering the time variation of the PMT gain. The observed number of solar neutrino events in 3.49-19.49 MeV electron kinetic energy region during SK-IV is 65,443-388+390(stat.)±925(syst.) events. Corresponding B8 solar neutrino flux is (2.314±0.014(stat.)±0.040(syst.))×106 cm-2 s-1, assuming a pure electron-neutrino flavor component without neutrino oscillations. The flux combined with all SK phases up to SK-IV is (2.336±0.011(stat.)±0.043(syst.))×106 cm-2 s-1. Based on the neutrino oscillation analysis from all solar experiments, including the SK 5805 days dataset, the best-fit neutrino oscillation parameters are sin2θ12,solar=0.306±0.013 and Δm21,solar2=(6.10-0.81+0.95)×10-5 eV2, with a deviation of about 1.5σ from the Δm212 parameter obtained by KamLAND. The best-fit neutrino oscillation parameters obtained from all solar experiments and KamLAND are sin2θ12,global=0.307±0.012 and Δm21,global2=(7.50-0.18+0.19)×10-5 eV2.

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Atmospheric neutrino oscillation analysis with neutron tagging and an expanded fiducial volume in Super-Kamiokande I-V

Wester T., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R., Friend M., Hasegawa T.

Physical Review D 109 ( 7 ) 2024.04

ISSN 24700010

We present a measurement of neutrino oscillation parameters with the Super-Kamiokande detector using atmospheric neutrinos from the complete pure-water SK I-V (April 1996-July 2020) dataset, including events from an expanded fiducial volume. The dataset corresponds to 6511.3 live days and an exposure of 484.2 kiloton-years. Measurements of the neutrino oscillation parameters Δm322, sin2θ23, sin2θ13, δCP, and the preference for the neutrino mass ordering are presented with atmospheric neutrino data alone, and with constraints on sin2θ13 from reactor neutrino experiments. Our analysis including constraints on sin2θ13 favors the normal mass ordering at the 92.3% level.

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Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos in the SK-Gd experiment

Sakai S., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Jang M.C., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Nakamura T., Jang J.S., Machado L.N., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Prouse N.W., Scott M., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., Langella A., De Rosa G., Collazuol G., Iacob F., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Okazaki R., Akutsu R.

Physical Review D 109 ( 1 ) 2024.01

ISSN 24700010

We report the first measurement of the atmospheric neutrino-oxygen neutral-current quasielastic (NCQE) cross section in the gadolinium-loaded Super-Kamiokande (SK) water Cherenkov detector. In June 2020, SK began a new experimental phase, named SK-Gd, by loading 0.011% by mass of gadolinium into the ultrapure water of the SK detector. The introduction of gadolinium to ultrapure water has the effect of improving the neutron-tagging efficiency. Using a 552.2 day dataset from August 2020 to June 2022, we measure the NCQE cross section to be 0.74±0.22(stat)-0.15+0.85(syst)×10-38 cm2/oxygen in the energy range from 160 MeV to 10 GeV, which is consistent with the atmospheric neutrino-flux-averaged theoretical NCQE cross section and the measurement in the SK pure-water phase within the uncertainties. Furthermore, we compare the models of the nucleon-nucleus interactions in water and find that the binary cascade model and the Liège intranuclear cascade model provide a somewhat better fit to the observed data than the Bertini cascade model. Since the atmospheric neutrino-oxygen NCQE reactions are one of the main backgrounds in the search for diffuse supernova neutrino background (DSNB), these new results will contribute to future studies - and the potential discovery - of the DSNB in SK.

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First measurement of muon neutrino charged-current interactions on hydrocarbon without pions in the final state using multiple detectors with correlated energy spectra at T2K

Abe K., Akhlaq N., Akutsu R., Alarakia-Charles H., Ali A., Alj Hakim Y.I., Alonso Monsalve S., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bordoni S., Boyd S.B., Bravar A., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Caballero J.A., Calabria N.F., Cao S., Carabadjac D., Carter A.J., Cartwright S.L., Casado M.P., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Chong P.S., Christodoulou G., Chvirova A., Cicerchia M., Coleman J., Collazuol G., Cook L., Cudd A., Dalmazzone C., Daret T., Dasgupta P., Davydov Y.I., De Roeck A., De Rosa G., Dealtry T., Delogu C.C., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Dygnarowicz K., Eguchi A., Emery-Schrenk S., Erofeev G., Ershova A., Eurin G., Fedorova D., Fedotov S., Feltre M., Finch A.J., Fiorentini Aguirre G.A., Fiorillo G., Fitton M.D., Franco Patiño J.M., Friend M., Fujii Y., Fukuda Y., Furui Y., Fusshoeller K., Giannessi L., Giganti C., Glagolev V., Gonin M., González Rosa J., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R.

Physical Review D 108 ( 11 ) 2023.12

ISSN 24700010

This paper reports the first measurement of muon neutrino charged-current interactions without pions in the final state using multiple detectors with correlated energy spectra at T2K. The data was collected on hydrocarbon targets using the off-axis T2K near detector (ND280) and the on-axis T2K near detector (INGRID) with neutrino energy spectra peaked at 0.6 GeV and 1.1 GeV, respectively. The correlated neutrino flux presents an opportunity to reduce the impact of the flux uncertainty and to study the energy dependence of neutrino interactions. The extracted double-differential cross sections are compared to several Monte Carlo neutrino-nucleus interaction event generators showing the agreement between both detectors individually and with the correlated result.

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Measurements of the νμ and ν ¯ μ -induced coherent charged pion production cross sections on C 12 by the T2K experiment

Abe K., Akhlaq N., Akutsu R., Ali A., Alonso Monsalve S., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bordoni S., Boyd S.B., Bravar A., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Caballero J.A., Calabria N.F., Cao S., Carabadjac D., Carter A.J., Cartwright S.L., Casado M.P., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Chong P.S., Christodoulou G., Chvirova A., Cicerchia M., Coleman J., Collazuol G., Cook L., Cudd A., Dalmazzone C., Daret T., Davydov Y.I., De Roeck A., De Rosa G., Dealtry T., Delogu C.C., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Dygnarowicz K., Eguchi A., Emery-Schrenk S., Erofeev G., Ershova A., Eurin G., Fedorova D., Fedotov S., Feltre M., Finch A.J., Fiorentini Aguirre G.A., Fiorillo G., Fitton M.D., Franco Patiño J.M., Friend M., Fujii Y., Fukuda Y., Furui Y., Giannessi L., Giganti C., Glagolev V., Gonin M., González Rosa J., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Harris D.A., Hartz M., Hasegawa T.

Physical Review D 108 ( 9 ) 2023.11

ISSN 24700010

We report an updated measurement of the νμ-induced, and the first measurement of the ν¯μ-induced coherent charged pion production cross section on C12 nuclei in the Tokai-to-Kamioka experiment. This is measured in a restricted region of the final-state phase space for which pμ,π>0.2 GeV, cos(θμ)>0.8 and cos(θπ)>0.6, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured νμ charged current coherent pion production flux-averaged cross section on C12 is (2.98±0.37(stat)±0.31(syst)-0.00+0.49(Q2 model))×10-40 cm2. The new measurement of the ν¯μ-induced cross section on C12 is (3.05±0.71(stat)±0.39(syst)-0.00+0.74(Q2 model))×10-40 cm2. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.

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Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6×1021 protons on target

Abe K., Akhlaq N., Akutsu R., Ali A., Alonso Monsalve S., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bordoni S., Boyd S.B., Bravar A., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Caballero J.A., Calabria N.F., Cao S., Carabadjac D., Carter A.J., Cartwright S.L., Casado M.P., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Chong P.S., Christodoulou G., Chvirova A., Cicerchia M., Coleman J., Collazuol G., Cook L., Cudd A., Dalmazzone C., Daret T., Davydov Y.I., De Roeck A., De Rosa G., Dealtry T., Delogu C.C., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Dygnarowicz K., Eguchi A., Emery-Schrenk S., Erofeev G., Ershova A., Eurin G., Fedorova D., Fedotov S., Feltre M., Finch A.J., Fiorentini Aguirre G.A., Fiorillo G., Fitton M.D., Franco Patiño J.M., Friend M., Fujii Y., Fukuda Y., Furui Y., Fusshoeller K., Giannessi L., Giganti C., Glagolev V., Gonin M., González Rosa J., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Harris D.A.

Physical Review D 108 ( 7 ) 2023.10

ISSN 24700010

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and nonstandard interactions can violate this symmetry. In this work we report the measurements of sin2θ23 and Δm322 independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of 1.97×1021 and 1.63×1021 protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross section models, new near-detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.

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Measurements of neutrino oscillation parameters from the T2K experiment using 3.6 × 10 21 protons on target

Abe K., Akhlaq N., Akutsu R., Ali A., Alonso Monsalve S., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bordoni S., Boyd S.B., Bravar A., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Caballero J.A., Calabria N.F., Cao S., Carabadjac D., Carter A.J., Cartwright S.L., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Chong P.S., Christodoulou G., Chvirova A., Cicerchia M., Coleman J., Collazuol G., Cook L., Cudd A., Dalmazzone C., Daret T., Davydov Y.I., De Roeck A., De Rosa G., Dealtry T., Delogu C.C., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Dygnarowicz K., Eguchi A., Emery-Schrenk S., Erofeev G., Ershova A., Eurin G., Fedorova D., Fedotov S., Feltre M., Finch A.J., Fiorentini Aguirre G.A., Fiorillo G., Fitton M.D., Franco Patiño J.M., Friend M., Fujii Y., Fukuda Y., Fusshoeller K., Giannessi L., Giganti C., Glagolev V., Gonin M., González Rosa J., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Harris D.A., Hartz M., Hasegawa T.

European Physical Journal C 83 ( 9 ) 2023.09

ISSN 14346044

The T2K experiment presents new measurements of neutrino oscillation parameters using 19.7 (16.3) × 10 20 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 4.7 × 10 20 POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on sin 2θ<inf>13</inf> and the impact of priors on the δ<inf>CP</inf> measurement. Both analyses prefer the normal mass ordering and upper octant of sin 2θ<inf>23</inf> with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin 2θ<inf>13</inf> from reactors, sin2θ23=0.561-0.032+0.021 using Feldman–Cousins corrected intervals, and Δm322=2.494-0.058+0.041×10-3eV2 using constant Δχ2 intervals. The CP-violating phase is constrained to δCP=-1.97-0.70+0.97 using Feldman–Cousins corrected intervals, and δ<inf>CP</inf>= 0 , π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2 σ credible level using a flat prior in δ<inf>CP</inf>, and just below 2 σ using a flat prior in sin δ<inf>CP</inf>. When the external constraint on sin 2θ<inf>13</inf> is removed, sin2θ13=28.0-6.5+2.8×10-3, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

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Search for Astrophysical Electron Antineutrinos in Super-Kamiokande with 0.01% Gadolinium-loaded Water

Harada M., Abe K., Bronner C., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Drapier O., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Choi K., Iovine N., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C.

Astrophysical Journal Letters 951 ( 2 ) 2023.07

ISSN 20418205

We report the first search result for the flux of astrophysical electron antineutrinos for energies(10)MeV in the gadolinium-loaded Super-Kamiokande (SK) detector. In 2020 June, gadolinium was introduced to the ultrapure water of the SK detector in order to detect neutrons more efficiently. In this new experimental phase, SK-Gd, we can search for electron antineutrinos via inverse beta decay with efficient background rejection thanks to the high efficiency of the neutron tagging technique. In this paper, we report the result for the initial stage of SK-Gd, during 2020 August 26, and 2022 June 1 with a 22.5 × 552 kton · day exposure at 0.01% Gd mass concentration. No significant excess over the expected background in the observed events is found for the neutrino energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90% confidence level. The limits and sensitivities are already comparable with the previous SK result with pure water (22.5 × 2970 kton · day) owing to the enhanced neutron tagging. Operation with Gd increased to 0.03% started in 2022 June.

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Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water

Shinoki M., Abe K., Hayato Y., Hiraide K., Hosokawa K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Lee S.H., Moon D.H., Park R.G., Bodur B., Scholberg K., Walter C.W., Beauchêne A., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Choi K., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Langella A., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L., Gonin M.

Physical Review D 107 ( 9 ) 2023.05

ISSN 24700010

Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic showers due to spallation in water, producing neutrons and radioactive isotopes. These are a major background source for studies of MeV-scale neutrinos and searches for rare events. In 2020, gadolinium was introduced into the ultra-pure water in the Super-Kamiokande detector to improve the detection efficiency of neutrons. In this study, the cosmogenic neutron yield was measured using data acquired during the period after the gadolinium loading. The yield was found to be (2.76±0.02(stat)±0.19(syst))×10-4 μ-1 g-1 cm2 at an average muon energy 259 GeV at the Super-Kamiokande detector.

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Search for Cosmic-Ray Boosted Sub-GeV Dark Matter Using Recoil Protons at Super-Kamiokande

Abe K., Hayato Y., Hiraide K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Xia J., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Choi K., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C., Maekawa Y., Nishimura Y., Friend M.

Physical Review Letters 130 ( 3 ) 2023.01

ISSN 00319007

We report a search for cosmic-ray boosted dark matter with protons using the 0.37 megaton×years data collected at Super-Kamiokande experiment during the 1996-2018 period (SKI-IV phase). We searched for an excess of proton recoils above the atmospheric neutrino background from the vicinity of the Galactic Center. No such excess is observed, and limits are calculated for two reference models of dark matter with either a constant interaction cross section or through a scalar mediator. This is the first experimental search for boosted dark matter with hadrons using directional information. The results present the most stringent limits on cosmic-ray boosted dark matter and exclude the dark matter-nucleon elastic scattering cross section between 10-33cm2 and 10-27cm2 for dark matter mass from 1 MeV/c2 to 300 MeV/c2.

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Neutron tagging following atmospheric neutrino events in a water Cherenkov detector

Abe K., Haga Y., Hayato Y., Hiraide K., Ieki K., Ikeda M., Imaizumi S., Iyogi K., Kameda J., Kanemura Y., Kataoka Y., Kato Y., Kishimoto Y., Miki S., Mine S., Miura M., Mochizuki T., Moriyama S., Nagao Y., Nakahata M., Nakajima T., Nakano Y., Nakayama S., Okada T., Okamoto K., Orii A., Sato K., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Tasaka S., Tomura T., Ueno K., Watanabe S., Yano T., Yokozawa T., Han S., Irvine T., Kajita T., Kametani I., Kaneyuki K., Lee K.P., McLachlan T., Okumura K., Richard E., Tashiro T., Wang R., Xia J., Megias G.D., Bravo-Berguño D., Labarga L., Zaldivar B., Goldhaber M., Blaszczyk F.D.M., Gustafson J., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Sussman S., Wan L., Wester T., Pointon B.W., Bian J., Carminati G., Elnimr M., Griskevich N.J., Kropp W.R., Locke S., Renshaw A., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hartfiel B.L., Hill J., Keig W.E., Hong N., Kim J.Y., Lim I.T., Park R.G., Akiri T., Bodur B., Himmel A., Li Z., O'Sullivan E., Scholberg K., Walter C.W., Wongjirad T., Bernard L., Coffani A., Drapier O., El Hedri S.

Journal of Instrumentation 17 ( 10 ) 2022.10

We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218±9 μs.

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Searching for Supernova Bursts in Super-Kamiokande IV

Mori M., Abe K., Hayato Y., Hiraide K., Ieki K., Ikeda M., Imaizumi S., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakano Y., Nakayama S., Noguchi Y., Okada T., Okamoto K., Orii A., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Tomiya T., Watanabe S., Yano T., Yoshida S., Han S., Kajita T., Okumura K., Tashiro T., Wang X., Xia J., Megias G.D., Bravo-Berguño D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Zsoldos S., Pointon B.W., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Paganini P., Quilain B., Santos A.D., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F.

Astrophysical Journal 938 ( 1 ) 2022.10

ISSN 0004637X

Super-Kamiokande has been searching for neutrino bursts characteristic of core-collapse supernovae continuously, in real time, since the start of operations in 1996. The present work focuses on detecting more distant supernovae whose event rate may be too small to trigger in real time, but may be identified using an offline approach. The analysis of data collected from 2008 to 2018 found no evidence of distant supernovae bursts. This establishes an upper limit of 0.29 yr-1 on the rate of core-collapse supernovae out to 100 kpc at 90% C.L. For supernovae that fail to explode and collapse directly to black holes the limit reaches to 300 kpc.

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Search for proton decay via p →μ+K0 in 0.37 megaton-years exposure of Super-Kamiokande

Matsumoto R., Abe K., Hayato Y., Hiraide K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Xia J., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Choi K., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ludovici L., Gonin M., Pronost G., Fujisawa C.

Physical Review D 106 ( 7 ) 2022.10

ISSN 24700010

We searched for proton decay via p→μ+K0 in 0.37 Mton·years of data collected between 1996 and 2018 from the Super-Kamiokande water Cherenkov experiment. The selection criteria were defined separately for KS0 and KL0 channels. No significant event excess has been observed. As a result of this analysis, which extends the previous search by an additional 0.2 Mton·years of exposure and uses an improved event reconstruction, we set a lower limit of 3.6×1033 years on the proton lifetime.

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Scintillator ageing of the T2K near detectors from 2010 to 2021

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bordoni S., Boyd S.B., Bravar A., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Calabria N.F., Cao S., Carter A.J., Cartwright S.L., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Cudd A., Davydov Y.I., De Roeck A., De Rosa G., Dealtry T., Delogu C.C., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Dygnarowicz K., Eguchi A., Emery-Schrenk S., Ershova A., Fedotov S., Fernandez P., Finch A.J., Fiorentini Aguirre G.A., Fiorillo G., Friend M., Fujii Y., Fukuda Y., Fusshoeller K., Giganti C., Glagolev V., Gonin M., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Harris D.A., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hatzikoutelis A., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Holin A., Holvey T.J., Hong Van N.T., Honjo T., Iacob F.

Journal of Instrumentation 17 ( 10 ) 2022.10

The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9-2.2% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator. The long component of the attenuation length of the wavelength shifting fibres was observed to degrade by 1.3-5.4% per year, while the short component of the attenuation length did not show any conclusive degradation.

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Pre-supernova Alert System for Super-Kamiokande

Machado L.N., Abe K., Hayato Y., Hiraide K., Ieki K., Ikeda M., Kameda J., Kanemura Y., Kaneshima R., Kashiwagi Y., Kataoka Y., Miki S., Mine S., Miura M., Moriyama S., Nakano Y., Nakahata M., Nakayama S., Noguchi Y., Okamoto K., Sato K., Sekiya H., Shiba H., Shimizu K., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., De Perio P., Martens K., Vagins M.R., Bian J., Griskevich N.J., Kropp W.R., Locke S., Smy M.B., Sobel H.W., Takhistov V., Yankelevich A., Han S., Kajita T., Okumura K., Tashiro T., Tomiya T., Wang X., Xia J., Yoshida S., Megias G.D., Fernandez P., Labarga L., Ospina N., Zaldivar B., Pointon B.W., Akutsu R., Gousy-Leblanc V., Hartz M., Konaka A., Prouse N.W., Kearns E., Raaf J.L., Wan L., Wester T., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Mueller T.A., Santos A.D., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Cao S., Choi K., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., De Rosa G., Collazuol G.

Astrophysical Journal 935 ( 1 ) 2022.08

ISSN 0004637X

In 2020, the Super-Kamiokande (SK) experiment moved to a new stage (SK-Gd) in which gadolinium (Gd) sulfate octahydrate was added to the water in the detector, enhancing the efficiency to detect thermal neutrons and consequently improving the sensitivity to low energy electron anti-neutrinos from inverse beta decay (IBD) interactions. SK-Gd has the potential to provide early alerts of incipient core-collapse supernovae through detection of electron anti-neutrinos from thermal and nuclear processes responsible for the cooling of massive stars before the gravitational collapse of their cores. These pre-supernova neutrinos emitted during the silicon burning phase can exceed the energy threshold for IBD reactions. We present the sensitivity of SK-Gd to pre-supernova stars and the techniques used for the development of a pre-supernova alarm based on the detection of these neutrinos in SK, as well as prospects for future SK-Gd phases with higher concentrations of Gd. For the current SK-Gd phase, high-confidence alerts for Betelgeuse could be issued up to 9 hr in advance of the core collapse itself.

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Search for solar electron anti-neutrinos due to spin-flavor precession in the Sun with Super-Kamiokande-IV

Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Yano T., Akutsu R., Han S., Kajita T., Okumura K., Tashiro T., Wang R., Xia J., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Pointon B.W., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., Hedri S.E., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Jakkapu M., Kobayashi T., Matsubara T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K.

Astroparticle Physics 139 2022.06

ISSN 09276505

Due to a very low production rate of electron anti-neutrinos (ν̄<inf>e</inf>) via nuclear fusion in the Sun, a flux of solar ν̄<inf>e</inf> is unexpected. An appearance of ν̄<inf>e</inf> in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (ν<inf>e</inf>→ν̄<inf>e</inf>) when neutrino has a finite magnetic moment. In this work, we have searched for solar ν̄<inf>e</inf> in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 ν̄<inf>e</inf> candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton⋅year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of 4.7×10−4 on the ν<inf>e</inf>→ν̄<inf>e</inf> conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade.

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Construction status and prospects of the Hyper-Kamiokande project

Itow Y., Abe K., Adrich P., Aihara H., Akutsu R., Alekseev I., Ali A., Alj Hakim Y.I., Ameli F., Anthony L.H.V., Araya A., Asaoka Y., Aushev V., Ballester F., Bandac I., Barbi M., Barr G., Batkiewicz-Kwasniak M., Bellato M., Berardi V., Bernard L., Bernardini E., Berns L., Bhadra S., Bian J., Blanchet A., Blondel A., Boiano A., Bolognesi S., Bonavera L., Booth N., Bordoni S., Borjabad S., Boschi T., Bose D., Boyd S.B., Bozza C., Bravar A., Bronner C., Brown L., Bubak A., Buchowicz A., Buizza Avanzini M., Cafagna F.S., Calabria N.F., Calvo-Mozota J.M., Cao S., Carroll A., Catanesi M.G., Cebriàn S., Chakraborty S., Choi J.H., Choubey S., Cicerchia M., Coleman J., Collazuol G., Cuen-Rochin S., Danilov M., Díaz López G., De la Fuente E., de Perio P., De Rosa G., Dealtry T., Densham C.J., Dergacheva A., Deshmukh N., Devi M.M., Di Lodovico F., Di Meo P., Di Palma I., Doyle T.A., Drakopoulou E., Drapier O., Dumarchez J., Eklund L., El Hedri S., Ellis J., Emery S., Esmaili A., Esteve R., Fedotov S., Feng J., Fernandez P., Fernández-Martinez E., Ferrario P., Ferrazzi B., Finch A., Finley C., Fiorillo G., Fitton M., Friend M., Fujii Y., Fujisawa C., Fukuda Y., Galinski G., Gao J., Garde C., Garfagnini A., Garode S., Gialanella L.

Proceedings of Science 395 2022.03

The Hyper-Kamiokande project is a 258-kton Water Cherenkov together with a 1.3-MW high-intensity neutrino beam from the Japan Proton Accelerator Research Complex (J-PARC). The inner detector with 186-kton fiducial volume is viewed by 20-inch photomultiplier tubes (PMTs) and multi-PMT modules, and thereby provides state-of-the-art of Cherenkov ring reconstruction with thresholds in the range of few MeVs. The project is expected to lead to precision neutrino oscillation studies, especially neutrino CP violation, nucleon decay searches, and low energy neutrino astronomy. In 2020, the project was officially approved and construction of the far detector was started at Kamioka. In 2021, the excavation of the access tunnel and initial mass production of the newly developed 20-inch PMTs was also started. In this paper, we present a basic overview of the project and the latest updates on the construction status of the project, which is expected to commence operation in 2027.

Prospects for neutrino astrophysics with Hyper-Kamiokande

Yano T., Abe K., Adrich P., Aihara H., Akutsu R., Alekseev I., Ali A., Alj Hakim Y.I., Ameli F., Anthony L.H.V., Araya A., Asaoka Y., Aushev V., Ballester F., Bandac I., Barbi M., Barr G., Batkiewicz-Kwasniak M., Bellato M., Berardi V., Bernard L., Bernardini E., Berns L., Bhadra S., Bian J., Blanchet A., Blondel A., Boiano A., Bolognesi S., Bonavera L., Booth N., Bordoni S., Borjabad S., Boschi T., Bose D., Boyd S.B., Bozza C., Bravar A., Bronner C., Brown L., Bubak A., Buchowicz A., Buizza Avanzini M., Cafagna F.S., Calabria N.F., Calvo-Mozota J.M., Cao S., Carroll A., Catanesi M.G., Cebriàn S., Chakraborty S., Choi J.H., Choubey S., Cicerchia M., Coleman J., Collazuol G., Cuen-Rochin S., Danilov M., Díaz López G., De la Fuente E., de Perio P., De Rosa G., Dealtry T., Densham C.J., Dergacheva A., Deshmukh N., Devi M.M., Di Lodovico F., Di Meo P., Di Palma I., Doyle T.A., Drakopoulou E., Drapier O., Dumarchez J., Eklund L., El Hedri S., Ellis J., Emery S., Esmaili A., Esteve R., Fedotov S., Feng J., Fernandez P., Fernández-Martinez E., Ferrario P., Ferrazzi B., Finch A., Finley C., Fiorillo G., Fitton M., Friend M., Fujii Y., Fujisawa C., Fukuda Y., Galinski G., Gao J., Garde C., Garfagnini A., Garode S., Gialanella L.

Proceedings of Science 395 2022.03

Hyper-Kamiokande is a multi-purpose next generation neutrino experiment. The detector is a two-layered cylindrical shape ultra-pure water tank, with its height of 64 m and diameter of 71 m. The inner detector will be surrounded by tens of thousands of twenty-inch photosensors and multi-PMT modules to detect water Cherenkov radiation due to the charged particles and provide our fiducial volume of 188 kt. This detection technique is established by Kamiokande and Super-Kamiokande. As the successor of these experiments, Hyper-K will be located deep underground, 600 m below Mt. Tochibora at Kamioka in Japan to reduce cosmic-ray backgrounds. Besides our physics program with accelerator neutrino, atmospheric neutrino and proton decay, neutrino astrophysics is an important research topic for Hyper-K. With its fruitful physics research programs, Hyper-K will play a critical role in the next neutrino physics frontier. It will also provide important information via astrophysical neutrino measurements, i.e., solar neutrino, supernova burst neutrinos and supernova relic neutrino. Here, we will discuss the physics potential of Hyper-K neutrino astrophysics.

Low energy radioactivity BG model in Super-Kamiokande detector from SK-IV data

Pronost G., Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okamoto K., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T.

Proceedings of Science 395 2022.03

The radioactivity background are among the most dangerous background for low energy neutrino analysis in Super-Kamiokande (SK), like the solar neutrino analysis. Among them, the main contribution is coming from 222Rn, which is spread in the detector’s water due to the water source and to the photo multiplier (PMT) emanations. Up to now, its exact distribution in the detector was not known. Using our knowledge of the radon concentration in the detector water, and the SK-IV solar data, we developed a model of the radon distribution in the detector. The uncertainty on the Rn concentration associated with this model was estimated to be ∼ 0.1 mBq/m3

Follow-up of GWTC-2 gravitational wave events with neutrinos from the Super-Kamiokande detector

Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okamoto K., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T.

Proceedings of Science 395 2022.03

Super-Kamiokande (SK) is a 50-kt water Cherenkov detector, instrumented with ∼ 13k photo-multipliers and running since 1996. It is sensitive to neutrinos with energies ranging from 4.5 MeV to several TeV. A new framework has been developed for the follow-up of gravitational wave (GW) alerts issued by the LIGO-Virgo collaboration (LVC). Neutrinos are searched for, using a 1000-second time window centered on the alert time and in both SK low-energy and high-energy samples. Such observation can then be used to constrain the neutrino emission from the GW source. The significance of potential signals has been obtained by comparing neutrino direction with the localization of the GW. The computation of limits on incoming neutrino flux and on the total energy emitted in neutrinos by the source has been performed for the different neutrino flavors. The results using the LVC GWTC-2 catalog (covering O3a period) are presented, as well as the outlooks for the future real-time public release of follow-ups for the O4 period (in 2022) and beyond.

Diffuse Supernova Neutrino Background search at Super-Kamiokande with neutron tagging

Giampaolo A., El Hedri S., Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okamoto K., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., Giampolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K.

Proceedings of Science 395 2022.03

Detecting the Diffuse Supernova Neutrino Background at Super-Kamiokande requires designing state-of-the-art background removal technique to reject radioactivity induced by cosmic muon spallation, and identify atmospheric neutrino interactions. Identifying the neutron produced by the interaction of DSNB antineutrinos would allow to remove most of these backgrounds, but is particularly challenging in pure water. With the advent of the SK-Gd era, with Gadolinium being dissolved in the SK water, the efficiency of the neutron tagging procedure will increase dramatically, and the SK experiment will make significant gains in its sensitivity to the DSNB. I will present the role of neutron tagging and the challenges it provides, as well as discuss the impact of the SK-Gd project.

Diffuse Supernova Neutrino Background Search at Super-Kamiokande

El Hedri S., Ashida Y., Giampaolo A., Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okamoto K., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Kearns E., Raaf J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., Gimpaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Cao S., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T., Nakadaira T., Nakamura K., Oyama Y.

Proceedings of Science 395 2022.03

We present the results of a search for the Diffuse Supernova Neutrino Background (DSNB) at Super-Kamiokande (SK) that incorporates 22.5 × 2970 kton.days of data from its fourth data-taking phase. Two analyses, with different energy regimes covering the 9.3−81.3 MeV antineutrino energy range, have been developed based on previous SK searches, with substantially improved background modeling and data reduction techniques. Moreover, a combined analysis of nearly 20 years of SK data (1996-2018) has been performed, with a 90% C.L. sensitivity to the DSNB flux comparable to various DSNB predictions. No significant evidence for a DSNB signal has been observed, and both analyses set world-leading limits on the DSNB flux that can reach about 2.7ν<inf>e</inf>.cm−2.s−1 for a wide range of models.

First gadolinium loading to Super-Kamiokande

Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Imaizumi S., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., Hedri S.E., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Cao S., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T.

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 1027 2022.03

ISSN 01689002

In order to improve Super-Kamiokande's neutron detection efficiency and to thereby increase its sensitivity to the diffuse supernova neutrino background flux, 13 tons of Gd<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>⋅8H<inf>2</inf>O (gadolinium sulfate octahydrate) was dissolved into the detector's otherwise ultrapure water from July 14 to August 17, 2020, marking the start of the SK-Gd phase of operations. During the loading, water was continuously recirculated at a rate of 60 m3/h, extracting water from the top of the detector and mixing it with concentrated Gd<inf>2</inf>(SO<inf>4</inf>)<inf>3</inf>⋅8H<inf>2</inf>O solution to create a 0.02% solution of the Gd compound before injecting it into the bottom of the detector. A clear boundary between the Gd-loaded and pure water was maintained through the loading, enabling monitoring of the loading itself and the spatial uniformity of the Gd concentration over the 35 days it took to reach the top of the detector. During the subsequent commissioning the recirculation rate was increased to 120 m3/h, resulting in a constant and uniform distribution of Gd throughout the detector and water transparency equivalent to that of previous pure-water operation periods. Using an Am–Be neutron calibration source the mean neutron capture time was measured to be 115±1 μs, which corresponds to a Gd concentration of 111±2 ppm, as expected for this level of Gd loading. This paper describes changes made to the water circulation system for this detector upgrade, the Gd loading procedure, detector commissioning, and the first neutron calibration measurements in SK-Gd.

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Diffuse supernova neutrino background search at Super-Kamiokande

Abe K., Bronner C., Hayato Y., Hiraide K., Ikeda M., Imaizumi S., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Xia J., Megias G.D., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Cao S., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Martin D., Scott M., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Mattiazzi M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Friend M., Hasegawa T., Ishida T., Kobayashi T., Jakkapu M., Matsubara T.

Physical Review D 104 ( 12 ) 2021.12

ISSN 24700010

We have conducted a new search for the diffuse supernova neutrino background (DSNB) flux at Super-Kamiokande (SK), with a 22.5×2970-kton·day exposure from its fourth operational phase IV. With the new analysis we improve on the existing background reduction techniques and systematic uncertainties and take advantage of an improved neutron tagging algorithm to lower the energy threshold compared to the previous phases of SK. This allows for setting the world's most stringent upper limit on the extraterrestrial ν¯e flux, for neutrino energies below 31.3 MeV. The SK-IV results are combined with the ones from the first three phases of SK to perform a joint analysis using 22.5×5823 kton·days of data. This analysis has the world's best sensitivity to the DSNB ν¯e flux, comparable to the predictions from various models. For neutrino energies larger than 17.3 MeV, the new combined 90% CL upper limits on the DSNB ν¯e flux lie around 2.7 cm-2·sec-1, strongly disfavoring the most optimistic predictions. Finally, potentialities of the gadolinium phase of SK and the future Hyper-Kamiokande experiment are discussed.

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Search for tens of MeV neutrinos associated with gamma-ray bursts in Super-Kamiokande

Orii A., Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Miura M., Moriyama S., Mochizuki T., Nagao Y., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Wang R., Xia J., Megias G.D., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Pointon B.W., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Matsuno S., Anthony L.H.V., Litchfield R.P., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T.

Progress of Theoretical and Experimental Physics 2021 ( 10 ) 2021.10

A search for neutrinos produced in coincidence with gamma-ray bursts (GRBs) was conducted with the Super-Kamiokande (SK) detector. Between December 2008 and March 2017, the Gamma-ray Coordinates Network recorded 2208 GRBs that occurred during normal SK operation. Several time windows around each GRB were used to search for coincident neutrino events. No statistically significant signal in excess of the estimated backgrounds was detected. The νe fluence in the range from 8 MeV to 100 MeV in positron total energy for νe+p → e++n was found to be less than 5.07 × 105 cm-2 per GRB at a 90% confidence level. For all GRBs, upper bounds were obtained on the fluence as a function of neutrino energy. Additionally, for GRBs at known distances, upper limits were set for the neutrino energy emission at the GRB.

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Search for neutrinos in coincidence with gravitational wave events from the LIGO–Virgo O3a observing run with the Super-Kamiokande detector

Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Kameda J., Kanemura Y., Kataoka Y., Miki S., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Watanabe S., Yano T., Han S., Kajita T., Okumura K., Tashiro T., Wang R., Xia J., Megias G.D., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Pointon B.W., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Bernard L., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Martin D.G.R., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., de Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Ludovici L., Maekawa Y., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Jakkapu M., Kobayashi T., Matsubara T., Nakadaira T.

Astrophysical Journal (Astrophysical Journal) 918 ( 2 ) 2021.09

ISSN 0004637X

The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO–Virgo Collaboration (LVC). Both low-energy (7–100 MeV) and high-energy (0.1–105 GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation, p-values were estimated using neutrino direction and LVC sky map; the most significant event (GW190602_175927) is associated with a post-trial p-value of 7.8% (1.4σ). Additionally, flux limits were computed independently for each sample and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors and for all flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.

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Supernova Model Discrimination with Hyper-Kamiokande

Abe K., Adrich P., Aihara H., Akutsu R., Alekseev I., Ali A., Ameli F., Anghel I., Anthony L.H.V., Antonova M., Araya A., Asaoka Y., Ashida Y., Aushev V., Ballester F., Bandac I., Barbi M., Barker G.J., Barr G., Batkiewicz-Kwasniak M., Bellato M., Berardi V., Bergevin M., Bernard L., Bernardini E., Berns L., Bhadra S., Bian J., Blanchet A., Blaszczyk F.D.M., Blondel A., Boiano A., Bolognesi S., Bonavera L., Booth N., Borjabad S., Boschi T., Bose D., Boyd S.B., Bozza C., Bravar A., Bravo-Berguo D., Bronner C., Brown L., Bubak A., Buchowicz A., Buizza Avanzini M., Cafagna F.S., Calabria N.F., Calvo-Mozota J.M., Cao S., Cartwright S.L., Carroll A., Catanesi M.G., Cebrian S., Chabera M., Chakraborty S., Checchia C., Choi J.H., Choubey S., Cicerchia M., Coleman J., Collazuol G., Cook L., Cowan G., Cuen-Rochin S., Danilov M., Díaz López G., De La Fuente E., De Perio P., De Rosa G., Dealtry T., Densham C.J., Dergacheva A., Deshmukh N., Devi M.M., Di Lodovico F., Di Meo P., Di Palma I., Doyle T.A., Drakopoulou E., Drapier O., Dumarchez J., Dunne P., Dziewiecki M., Eklund L., El Hedri S., Ellis J., Emery S., Esmaili A., Esteve R., Evangelisti A., Feely M., Fedotov S., Feng J., Fernandez P., Fernández-Martinez E., Ferrario P., Ferrazzi B., Feusels T.

Astrophysical Journal (Astrophysical Journal) 916 ( 1 ) 2021.07

ISSN 0004637X

Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants - neutron stars and black holes - are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations toward a precise reproduction of the explosion mechanism observed in nature.

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First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single- π+ production channel containing at least one proton

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berns L., Bhadra S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chakrani J., Cherdack D., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., De Rosa G., Dealtry T., Delogu C.C., Dennis S.R., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Douqa D., Doyle T.A., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Finch A.J., Fiorillo G., Francois C., Friend M., Fujii Y., Fukuda R., Fukuda Y., Fusshoeller K., Giganti C., Gonin M., Goodman E.A.G., Gorin A., Grassi M., Guigue M., Hadley D.R., Hamacher-Baumann P., Harris D.A., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Honjo T., Iacob F., Ichikawa A.K., Ikeda M., Ishida T., Ishitsuka M., Iwamoto K., Izmaylov A., Izumi N., Jakkapu M., Jamieson B.

Physical Review D (Physical Review D) 103 ( 11 ) 2021.06

ISSN 24700010

This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-π+ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single π+ and at least one proton in the final state, at the ND280 off axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models that have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.

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Improved constraints on neutrino mixing from the T2K experiment with 3.13×1021 protons on target

Physical Review D (Physical Review D) 103 ( 11 ) 2021.06

ISSN 24700010

The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of 14.9(16.4)×1020 protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the Pontecorvo-Maki-Nakagawa-Sakata parameters. For fits including a constraint on sin2θ13 from reactor data and assuming normal mass ordering T2K measures sin2θ23=0.53-0.04+0.03 and Δm322=(2.45±0.07)×10-3 eV2 c-4. The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper sin2θ23 octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the 2σ level.

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Measurements of and + charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berns L., Bhadra S., Bienstock S., Blanchet A., Blondel A., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Dergacheva A., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Gameil K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Harris D.A.

Progress of Theoretical and Experimental Physics 2021 ( 4 ) 2021.04

We report measurements of the flux-integrated and + charged-current cross-sections on water and hydrocarbon targets using the T2K anti-neutrino beam with a mean beam energy of 0.86 GeV. The signal is defined as the (anti-)neutrino charged-current interaction with one induced and no detected charged pion or proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton Module. The phase space of muons is restricted to the high-detection efficiency region, 400 and 30 , in the laboratory frame. An absence of pions and protons in the detectable phase spaces of 200, 70 and 600, 70 is required. In this paper, both the; cross-sections and +; cross-sections on water and hydrocarbon targets and their ratios are provided by using the D'Agostini unfolding method. The results of the integrated ; cross-section measurements over this phase space are ;\sigma{\rm H{2}O}=(1.082\pm0.068(\rm stat.) {+0.145}{-0.128}(\rm syst.)) \times 10 {-39}\,{\rm cm {2} / nucleon};, ;\sigma{\rm CH}=(1.096\pm0.054(\rm stat.) {+0.132}{-0.117}(\rm syst.)) \times 10 {-39}\,{\rm cm {2} / nucleon};, and ;\sigma{\rm H{2}O}/\sigma{\rm CH} = 0.987\pm0.078(\rm stat.) {+0.093}{-0.090}(\rm syst.);. The +; cross-section is ;\sigma{\rm H{2}O} = (1.155\pm0.064(\rm stat.) {+0.148}{-0.129}(\rm syst.)) \times 10 {-39}\,{\rm cm {2} / nucleon};, ;\sigma{\rm CH}=(1.159\pm0.049(\rm stat.) {+0.129}{-0.115}(\rm syst.)) \times 10 {-39}\,{\rm cm {2} / nucleon};, and ;\sigma{\rm H{2}O}/\sigma{\rm CH}=0.996\pm0.069(\rm stat.) {+0.083}{-0.078}(\rm syst.);.

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T2K measurements of muon neutrino and antineutrino disappearance using 3.13×1021 protons on target

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Antonova M., Aoki S., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berns L., Bhadra S., Blondel A., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Cherdack D., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., De Rosa G., Dealtry T., Delogu C.C., Dennis S.R., Densham C., Dergacheva A., Di Lodovico F., Dolan S., Doyle T.A., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Finch A.J., Fiorentini G.A., Francois C., Friend M., Fujii Y., Fukuda R., Fukuda Y., Fusshoeller K., Giganti C., Gonin M., Gorin A., Guigue M., Hadley D.R., Hamacher-Baumann P., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Honjo T., Iacob F., Ichikawa A.K., Ikeda M., Ishida T., Ishitsuka M., Iwamoto K., Izmaylov A., Izumi N., Jakkapu M., Jamieson B., Jenkins S.J., Jesús-Valls C., Jonsson P., Jung C.K., Jurj P.B., Kabirnezhad M.

Physical Review D (Physical Review D) 103 ( 1 ) 2021.01

ISSN 24700010

We report measurements by the T2K experiment of the parameters θ23 and Δm322, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K's neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from 1.49×1021 protons on target (POT) in neutrino mode and 1.64×1021 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin2(θ23)=0.51-0.07+0.06(0.43-0.05+0.21) and Δm322=2.47-0.09+0.08(2.50-0.13+0.18)×10-3 eV2/c4 for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take nonphysical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.

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Neutron-antineutron oscillation search using a 0.37 megaton-years exposure of Super-Kamiokande

Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Miura M., Moriyama S., Nagao Y., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Takenaka A., Tanaka H., Yano T., Akutsu R., Han S., Kajita T., Okumura K., Tashiro T., Wang R., Xia J., Bravo-Berguño D., Labarga L., Marti L., Zaldivar B., Blaszczyk F.D.M., Kearns E., Gustafson J.D., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Anthony L.H.V., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Matsubara T., Nakadaira T., Jakkapu M., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T.

Physical Review D (Physical Review D) 103 ( 1 ) 2021.01

ISSN 24700010

As a baryon number violating process with ΔB=2, neutron-antineutron oscillation (n→n¯) provides a unique test of baryon number conservation. We have performed a search for n→n¯ oscillation with bound neutrons in Super-Kamiokande, with the full dataset from its first four run periods, representing an exposure of 0.37 Mton-years. The search used a multivariate analysis trained on simulated n→n¯ events and atmospheric neutrino backgrounds and resulted in 11 candidate events with an expected background of 9.3 events. In the absence of statistically significant excess, we derived a lower limit on n¯ appearance lifetime in O16 nuclei of 3.6×1032 years and on the neutron-antineutron oscillation time of τn→n¯>4.7×108 s at 90% C.L.

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Performance of 50 cm Photomultiplier Tube for Hyper-Kamiokande

Maekawa Y., Fujisawa C., Nishimura Y.

2021 IEEE Nuclear Science Symposium and Medical Imaging Conference Record NSS Mic 2021 and 28th International Symposium on Room Temperature Semiconductor Detectors Rtsd 2022 2021

We developed a 50 cm-diameter photomultiplier tube (PMT) for Hyper-Kamiokande, which is a large water Cherenkov detector in Japan aiming at neutrino and nucleon-decay research by using forty thousand photosensors. The PMT, R12860 manufactured by Hamamatsu Photonics K.K. (Hamamatsu), achieved a double detection efficiency, reduced timing and charge resolutions as well as sufficient mechanical strength compared with a prior 50 cm PMT, R3600 for Super-Kamiokande. In 2018 over a hundred of the R12860 PMTs were installed in Super-Kamiokande, where we evaluated the performance together with the R3600 PMTs. The collection efficiency reached 95% with a higher quantum efficiency (QE) of 33% typical at peak of wavelength around 400 nm. Charge resolution was evaluated to be 27% in standard deviation and time resolution to be 1.5 nanoseconds in FWHM. Finally, noise reduction succeeded with clean materials and low dark count rate.

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Search for proton decay via p →e+π0 and p →μ+π0 with an enlarged fiducial volume in Super-Kamiokande I-IV

Takenaka A., Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nagao Y., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Suzuki Y., Takeda A., Takemoto Y., Tanaka H., Yano T., Akutsu R., Han S., Kajita T., Okumura K., Tashiro T., Wang R., Xia J., Bravo-Berguño D., Labarga L., Fernandez P., Zaldivar B., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Pointon B.W., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Mueller T.A., Paganini P., Quilain B., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Matsuno S., Anthony L.H.V., Litchfield R.P., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., Machado L.N., De Rosa G., Collazuol G., Iacob F., Lamoureux M., Ospina N., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Jakkapu M.

Physical Review D (Physical Review D) 102 ( 11 ) 2020.12

ISSN 24700010

We have searched for proton decay via p→e+π0 and p→μ+π0 modes with the enlarged fiducial volume data of Super-Kamiokande from April 1996 to May 2018, which corresponds to 450 kton·years exposure. We have accumulated about 25% more livetime and enlarged the fiducial volume of the Super-Kamiokande detector from 22.5 kton to 27.2 kton for this analysis, so that 144 kton·years of data, including 78 kton·years of additional fiducial volume data, has been newly analyzed. No candidates have been found for p→e+π0 and one candidate remains for p→μ+π0 in the conventional 22.5 kton fiducial volume and it is consistent with the atmospheric neutrino background prediction. We set lower limits on the partial lifetime for each of these modes: τ/B(p→e+π0)>2.4×1034 years and τ/B(p→μ+π0)>1.6×1034 years at 90% confidence level.

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Indirect search for dark matter from the Galactic Center and halo with the Super-Kamiokande detector

Abe K., Bronner C., Haga Y., Hayato Y., Ikeda M., Imaizumi S., Ito H., Iyogi K., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nagao Y., Nakahata M., Nakajima Y., Nakajima T., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Tasaka S., Tomura T., Ueno K., Yano T., Yokozawa T., Akutsu R., Han S., Irvine T., Kajita T., Kametani I., Lee K.P., Mclachlan T., Okumura K., Richard E., Tashiro T., Wang R., Xia J., Bravo-Berguño D., Labarga L., Fernandez P., Blaszczyk F.D.M., Gustafson J., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Sussman S., Wan L., Wester T., Berkman S., Tobayama S., Bian J., Carminati G., Elnimr M., Griskevich N.J., Kropp W.R., Locke S., Mine S., Renshaw A., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Hartfiel B.L., Hill J., Keig W.E., Hong N., Kim J.Y., Lim I.T., Park R.G., Akiri T., Bodur B., Himmel A., Li Z., O'sullivan E., Scholberg K., Walter C.W., Wongjirad T., Coffani A., Drapier O., El Hedri S., Giampaolo A., Gonin M., Imber J., Mueller T.A., Paganini P., Quilain B., Ishizuka T.

Physical Review D (Physical Review D) 102 ( 7 ) 2020.10

ISSN 24700010

We present a search for an excess of neutrino interactions due to dark matter in the form of weakly interacting massive particles (WIMPs) annihilating in the Galactic center or halo based on the data set of Super-Kamiokande-I, -II, -III and -IV taken from 1996 to 2016. We model the neutrino flux, energy, and flavor distributions assuming WIMP self-annihilation is dominant to νν¯, μ+μ-, bb¯, or W+W-. The excess is in comparison to atmospheric neutrino interactions which are modeled in detail and fit to data. Limits on the self-annihilation cross section σ are derived for WIMP masses in the range 1 GeV to 10 TeV, reaching as low as 9.6×10-23 cm3 s-1 for 5 GeV WIMPs in bb¯ mode and 1.2×10-24 cm3 s-1 for 1 GeV WIMPs in νν¯ mode. The obtained sensitivity of the Super-Kamiokande detector to WIMP masses below several tens of GeV is the best among similar indirect searches to date.

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Measurement of the charged-current electron (anti-)neutrino inclusive cross-sections at the T2K off-axis near detector ND280

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayashino T.

Journal of High Energy Physics (Journal of High Energy Physics) 2020 ( 10 ) 2020.10

The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp and dσ/d cos(θ), and the total cross-sections in a limited phase-space in momentum and scattering angle (p > 300 MeV/c and θ ≤ 45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.

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First measurement of the charged current ν ¯ μ double differential cross section on a water target without pions in the final state FIRST MEASUREMENT of the CHARGED CURRENT ... ABE K. et al.

Abe K., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Dumarchez J., Dunne P., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Gameil K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Iacob F., Ichikawa A.K., Ikeda M., Ishida T., Ishii T., Ishitsuka M.

Physical Review D (Physical Review D) 102 ( 1 ) 2020.07

ISSN 24700010

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First combined measurement of the muon neutrino and antineutrino charged-current cross section without pions in the final state at T2K

Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayashino T.

Physical Review D (Physical Review D) 101 ( 11 ) 2020.06

ISSN 24700010

This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8×1020 and 6.3×1020 protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference, and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.

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Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K

Zykova A., Abe K., Akhlaq N., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berns L., Bhadra S., Bienstock S., Bolognesi S., Bonus T., Bourguille B., Boyd S.B., Bravar A., Bravo Berguño D., Bronner C., Bron S., Bubak A., Buizza Avanzini M., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Cherdack D., Chikuma N., Christodoulou G., Cicerchia M., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Finch A.J., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Giganti C., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Honjo T., Iacob F., Ichikawa A.K., Ikeda M., Ishida T., Ishitsuka M.

Physical Review D (Physical Review D) 101 ( 11 ) 2020.06

ISSN 24700010

This paper reports the first simultaneous measurement of the double differential muon neutrino charged-current cross section on oxygen and carbon without pions in the final state as a function of the outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models' ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillation analyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV. The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.

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Search for Electron Antineutrino Appearance in a Long-Baseline Muon Antineutrino Beam

Abe K., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bravo Berguño D., Bronner C., Bubak A., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Gameil K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T.

Physical Review Letters (Physical Review Letters) 124 ( 16 ) 2020.04

ISSN 00319007

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.

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Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

Abe K., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Arihara T., Asada Y., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barrow D., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Berguño D.B., Bronner C., Bubak A., Avanzini M.B., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Cicerchia M., Christodoulou G., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Doyle T.A., Drapier O., Dumarchez J., Dunne P., Eguchi A., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Fusshoeller K., Gameil K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hassani S., Hastings N.C., Hayashino T., Hayato Y.

Nature (Nature) 580 ( 7803 ) 339 - 344 2020.04

ISSN 00280836

The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model’s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7–9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

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Evaluation of gadolinium's action on water Cherenkov detector systems with EGADS

Marti L., Ikeda M., Kato Y., Kishimoto Y., Nakahata M., Nakajima Y., Nakano Y., Nakayama S., Okajima Y., Orii A., Pronost G., Sekiya H., Shiozawa M., Tanaka H., Ueno K., Yamada S., Yano T., Yokozawa T., Murdoch M., Schuemann J., Vagins M.R., Bays K., Carminati G., Griskevich N.J., Kropp W.R., Locke S., Renshaw A., Smy M.B., Weatherly P., Ito S., Ishino H., Kibayashi A., Koshio Y., Mori T., Sakuda M., Yamaguchi R., Fernandez P., Labarga L., Bandac I., Perez J., Amey J., Litchfield R.P., Sztuc A., Uchida Y., Ma W.Y., Goldsack A., Simpson C., Wark D., Anthony L.H.V., McCauley N., Pritchard A., Di Lodovico F., Richards B., Cole A., Thiesse M., Thompson L., Imber J., Cao S.V., Ito K., Takeuchi Y., Akutsu R., Nishimura Y., Okumura K., Hirota S., Muto F., Yokoyama M., Suda Y., Zhang H.

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment) 959 2020.04

ISSN 01689002

Used for both proton decay searches and neutrino physics, large water Cherenkov (WC) detectors have been very successful tools in particle physics. They are notable for their large masses and charged particle detection capabilities. While current WC detectors reconstruct charged particle tracks over a wide energy range, they cannot efficiently detect neutrons. Gadolinium (Gd) has the largest thermal neutron capture cross section of all stable nuclei and produces an 8 MeV gamma cascade that can be detected with high efficiency. Because of the many new physics opportunities that neutron tagging with a Gd salt dissolved in water would open up, a large-scale R&D program called EGADS was established to demonstrate this technique's feasibility. EGADS features all the components of a WC detector, chiefly a 200-ton stainless steel water tank furnished with 240 photo-detectors, DAQ, and a water system that removes all impurities from water while keeping Gd in solution. In this paper we discuss the milestones towards demonstrating the feasibility of this novel technique, and the features of EGADS in detail.

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New large aperture photodetectors for water Cherenkov detectors

Nishimura Y.

ISSN 01689002

New 50cm-diameter photo-detectors based on three different types of amplification systems were developed for future large water Cherenkov detectors. The R12860 PMT, based on a box-and-line dynode, was developed with Hamamatsu Photonics K.K. (Hamamatsu). Its detection efficiency is twice that of a conventional 50 cm PMT, while also improving by a factor two the charge and timing resolutions and being able to resist pressures up to 1.25MPa. A 50 cm hybrid photo-detector (HPD) using an avalanche diode (Hamamatsu, R12850) realized further improvement on the resolutions by the successful development of a preamplifier. It requires higher bias voltage (eight kilovolts), which lead to the development of a built-in power supply or water tight connector. Finally, a 50-cm micro-channel plate PMT (GDB-6203) was developed for water Cherenkov detectors by North Night Vision Technology Co., LTD in China. It is based on the GDB-6201 model, with improved timing performances. The charge resolutions for single photoelectron of the R12860, R12850 and GDB-6203 PMTs were evaluated to be 35%, 15%, and 40% (standard deviation), while the transit time spreads measured for single photoelectrons at a fixed threshold were 4.1, 3.6 and 4.3 nsec (FWHM) respectively. We obtained operational waterproof designs for all those photodetectors.

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Basic studies of 3-inch PMT for multi-PMT development

Inomoto M., Ishitsuka M., Kuze M., Nishimura Y., Quilain B.

Journal of Physics: Conference Series (Journal of Physics: Conference Series) 1468 ( 1 ) 2020.03

ISSN 17426588

Hyper-Kamiokande is the next generation large-scale water Cherenkov detector. In Hyper-Kamiokade and Intermediate Water Cherenkov Detector for its long baseline project with J-PARC neutrino beam, use of multi-PMT, which is made by combination of 3-inch PMTs, is being considered. As part of multi-PMT development, we measured the characteristics of the 3-inch PMT including the temperature dependence of dark noise rate. The dark noise rate is important characteristic for detection of low energy events including neutron tagging. In addition, since PMT is generally susceptible to the magnetic field, we confirmed the photon detection efficiency in the condition where the magnetic field was applied.

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Evaluation of position dependent performance of 3-inch PMTs for Multi-PMT development

Izumi N., Ishitsuka M., Kuze M., Nishimura Y., Quilain B.

Journal of Physics: Conference Series (Journal of Physics: Conference Series) 1468 ( 1 ) 2020.03

ISSN 17426588

Hyper-Kamiokande detector is proposed as a next generation underground water Cherenkov detector in Japan, and is planned to be an order of magnitude bigger than its predecessor, Super-Kamiokande. In order to further improve the detector capabilities in both low and high energy sectors, the multi-PMT modules instrumented with multiple 3-inch PMTs are being developed, in addition to the improved high quantum efficiency 20-inch PMTs. We developed a moveable laser system that can illuminate different positions on the photocathode to measure the characterization of the 3-inch PMTs as a function of the position on the photocathode.

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Development and performance of the 20" PMT for Hyper-Kamiokande

Bronner C., Nishimura Y., Xia J., Tashiro T.

Journal of Physics: Conference Series (Journal of Physics: Conference Series) 1468 ( 1 ) 2020.03

ISSN 17426588

The inner detector of the future Hyper-Kamiokande experiment will be instrumented with 40000 20" photo-multiplier tubes (PMTs). Two models of PMTs are considered: the R12860 from Hamamatsu Photonics (nominal option), and the GDB-6203 from North Night Vision Technology (alternative option). Both models show improved performances compared to the PMTs used in the currently running Super-Kamiokande experiment. We present here the measurements of the performance of the nominal and alternative option PMTs done in the context of the Hyper-Kamiokande project, as well as the first use of those new PMTs in a running experiment, and other on-going developments for their future use in the Hyper-Kamiokande detector.

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Search for proton decay into three charged leptons in 0.37 megaton-years exposure of the Super-Kamiokande

Tanaka M., Abe K., Bronner C., Hayato Y., Ikeda M., Imaizumi S., Ito H., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Yano T., Akutsu R., Kajita T., Okumura K., Wang R., Xia J., Bravo-Bergunõ D., Labarga L., Fernandez P., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Coffani A., Drapier O., El Hedri S., Gonin M., Mueller T.A., Paganini P., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Matsuno S., Litchfield R.P., Sztuc A.A., Uchida Y., Berardi V., Catanesi M.G., Radicioni E., Calabria N.F., De Rosa G., Collazuol G., Iacob F., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Hasegawa M., Isobe Y., Miyabe H., Nakano Y., Shiozawa T., Sugimoto T., Suzuki A.T.

Physical Review D (Physical Review D) 101 ( 5 ) 2020.03

ISSN 24700010

A search for proton decay into three charged leptons has been performed by using 0.37 Mton·years of data collected in Super-Kamiokande. All possible combinations of electrons, muons, and their antiparticles consistent with charge conservation were considered as decay modes. No significant excess of events has been found over the background, and lower limits on the proton lifetime divided by the branching ratio have been obtained. The limits range between 9.2×1033 and 3.4×1034 years at 90% confidence level, improving by more than an order of magnitude upon limits from previous experiments. A first limit has been set for the p→μ-e+e+ mode.

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Measurement of the muon neutrino charged-current single π+ production on hydrocarbon using the T2K off-axis near detector ND280

Abe K., Akutsu R., Ali A., Alt C., Amey J., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Atkin E.T., Awataguchi Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bordoni S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Calland R.G., Campbell T., Cao S., Cartwright S.L., Castillo R., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Gameil K., Garcia A., Giganti C., Gizzarelli F., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haegel L., Haigh J.T., Hamacher-Baumann P., Hansen D., Harada J., Hartz M., Hasegawa T., Hastings N.C.

Physical Review D (Physical Review D) 101 ( 1 ) 2020.01

ISSN 24700010

We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using 5.56×1020 protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be σ=(11.76±0.44(stat)±2.39(syst))×10-40 cm2 nucleon-1. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.

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Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation γ rays

Abe K., Akutsu R., Ali A., Alt C., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Atkin E.T., Awataguchi Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Beloshapkin A., Bench F., Berardi V., Berkman S., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bravo Bergunõ D., Bronner C., Bubak A., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Cook L., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Dumarchez J., Dunne P., Eklund L., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda R., Fukuda Y., Gameil K., Giganti C., Golan T., Gonin M., Gorin A., Guigue M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Iacob F., Ichikawa A.K., Ikeda M., Ishida T.

Physical Review D (Physical Review D) 100 ( 11 ) 2019.12

ISSN 24700010

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Search for Astronomical Neutrinos from Blazar TXS 0506+056 in Super-Kamiokande

Hagiwara K., Abe K., Bronner C., Hayato Y., Ikeda M., Ito H., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Yano T., Akutsu R., Kajita T., Okumura K., Wang R., Xia J., Bravo-Berguño D., Labarga L., Fernandez P., Blaszczyk F.D.M., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Coffani A., Drapier O., Gonin M., Mueller T.A., Paganini P., Ishizuka T., Nakamura T., Jang J.S., Learned J.G., Matsuno S., Litchfield R.P., Sztuc A.A., Uchida Y., Berardi V., Calabria N.F., Catanesi M.G., Radicioni E., De Rosa G., Collazuol G., Iacob F., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Hasegawa M., Isobe Y., Miyabe H., Nakano Y., Shiozawa T., Sugimoto T., Suzuki A.T., Takeuchi Y.

Astrophysical Journal Letters (Astrophysical Journal Letters) 887 ( 1 ) 2019.12

ISSN 20418205

We report a search for astronomical neutrinos in the energy region from several GeV to TeV in the direction of the blazar TXS 0506+056 using the Super-Kamiokande detector following the detection of a 100 TeV neutrinos from the same location by the IceCube collaboration. Using Super-Kamiokande neutrino data across several data samples observed from 1996 April to 2018 February we have searched for both a total excess above known backgrounds across the entire period as well as localized excesses on smaller timescales in that interval. No significant excess nor significant variation in the observed event rate are found in the blazar direction. Upper limits are placed on the electron-and muon-neutrino fluxes at the 90% confidence level as 6.0 × 10-7 and 4.5 × 10-7-9.3 × 10-10 [erg cm-2 s-1], respectively.

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Sensitivity of Super-Kamiokande with Gadolinium to Low Energy Antineutrinos from Pre-supernova Emission

Simpson C., Abe K., Bronner C., Hayato Y., Ikeda M., Ito H., Iyogi K., Kameda J., Kataoka Y., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nakahata M., Nakajima Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Yano T., Akutsu R., Kajita T., Okumura K., Wang R., Xia J., Bravo-Berguo D., Labarga L., Fernandez P., Blaszczyk F.D.M., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Wan L., Wester T., Sussman S., Berkman S., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Coffani A., Drapier O., Gonin M., Imber J., Mueller T.A., Paganini P., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Litchfield R.P., Sztuc A.A., Uchida Y., Wascko M.O., Berardi V., Calabria N.F., Catanesi M.G., Intonti R.A., Radicioni E., Rosa G.D., Collazuol G., Iacob F., Ludovici L., Nishimura Y., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T.

Astrophysical Journal (Astrophysical Journal) 885 ( 2 ) 2019.11

ISSN 0004637X

Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova (CCSN) will be preceded by an increasing flux of neutrinos and antineutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent CCSN, hours earlier than the detection of the neutrinos from core collapse. Electron antineutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximizing detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hr before core collapse for a 15-25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, α-Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hr before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.

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Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors

Abe K., Akutsu R., Ali A., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Awataguchi Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda Y., Gameil K., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Hosomi F., Ichikawa A.K., Ikeda M., Inoue T., Intonti R.A., Ishida T., Ishii T., Ishitsuka M., Iwamoto K., Izmaylov A.

Progress of Theoretical and Experimental Physics (Progress of Theoretical and Experimental Physics) 2019 ( 9 ) 2019.09

We report a measurement of the flux-integrated νμ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are σH2oCC = (0.840±0.010(stat.)+0.10-0.08(syst.)) ×10-38 cm2/nucleon, σCHCC = (0.817±0.007(stat.)+0.11-0.08(syst.)) × 10-38 cm2/nucleon, and σFeCC = (0.859±0.003(stat.)^+0.12-0.10(syst.)) ×10-38 cm2/nucleon, respectively, for a restricted phase space of induced muons: θμ < 45° and pμ > 0.4 GeV/c in the laboratory frame. The measured cross section ratios are σH2oCC/σCHCC = 1.028±0.016(stat.)±0.053(syst.), σFeCC/σH2oCC = 1.023±0.012(stat.)±0.058(syst.), and σFeCC/σCHCC = 1.049±0.010(stat.)±0.043(syst.). These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.

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Search for heavy neutrinos with the T2K near detector ND280

Abe K., Akutsu R., Ali A., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Awataguchi Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., de Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda Y., Gameil K., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haegel L., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Hosomi F., Iacob F., Ichikawa A.K., Ikeda M., Inoue T., Intonti R.A., Ishida T., Ishii T., Ishitsuka M.

Physical Review D (Physical Review D) 100 ( 5 ) 2019.09

ISSN 24700010

This paper reports on the search for heavy neutrinos with masses in the range 140<MN<493 MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→ℓα±π and N→ℓα+ℓβ-ν(-)(α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavored currents (Ue2, Uμ2, Uτ2) as a function of the heavy neutrino mass, e.g., Ue2<10-9 at 90% C.L. for a mass of 390 MeV/c2. These constraints are competitive with previous experiments.

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Atmospheric neutrino oscillation analysis with improved event reconstruction in Super-Kamiokande IV

Jiang M., Abe K., Bronner C., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nakahata M., Nakajima Y., Nakano Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Yano T., Akutsu R., Kajita T., Nishimura Y., Okumura K., Wang R., Xia J., Labarga L., Fernandez P., Blaszczyk F.D.M., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sussman S., Berkman S., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Weatherly P., Smy M.B., Sobel H.W., Takhistov V., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Gonin M., Imber J., Mueller T.A., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Litchfield R.P., Uchida Y., Wascko M.O., Calabria N.F., Catanesi M.G., Intonti R.A., Radicioni E., De Rosa G., Ali A., Collazuol G., Iacob F., Ludovici L., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K., Hasegawa M., Isobe Y., Miyabe H., Sugimoto T., Suzuki A.T., Takeuchi Y., Ashida Y.

Progress of Theoretical and Experimental Physics (Progress of Theoretical and Experimental Physics) 2019 ( 5 ) 2019.05

A new event reconstruction algorithm based on a maximum likelihood method has been developed for Super-Kamiokande. Its improved kinematic and particle identification capabilities enable the analysis of atmospheric neutrino data in a detector volume 32% larger than previous analyses and increase the sensitivity to the neutrino mass hierarchy.Analysis of a 253.9 kton•year exposure of the Super-Kamiokande IV atmospheric neutrino data has yielded a weak preference for the normal hierarchy, disfavoring the inverted hierarchy at 74% assuming oscillations at the best fit of the analysis.

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Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km

Abe K., Akutsu R., Ali A., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Awataguchi Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda Y., Gameil K., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Hosomi F., Iacob F., Ichikawa A.K., Ikeda M., Inoue T., Intonti R.A., Ishida T., Ishii T., Ishitsuka M., Iwamoto K.

Physical Review D (Physical Review D) 99 ( 7 ) 2019.04

ISSN 24700010

We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin2θ24 for the sterile neutrino mass splitting Δm412<3×10-3 eV2/c4.

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Measurement of the neutrino-oxygen neutral-current quasielastic cross section using atmospheric neutrinos at Super-Kamiokande

Wan L., Abe K., Bronner C., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Mochizuki T., Nakahata M., Nakajima Y., Nakano Y., Nakayama S., Okada T., Okamoto K., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Yano T., Akutsu R., Kajita T., Nishimura Y., Okumura K., Wang R., Xia J., Labarga L., Fernandez P., Blaszczyk F.D.M., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sussman S., Berkman S., Bian J., Griskevich N.J., Kropp W.R., Locke S., Mine S., Weatherly P., Smy M.B., Sobel H.W., Takhistov V., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Bodur B., Scholberg K., Walter C.W., Gonin M., Imber J., Mueller T.A., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Litchfield R.P., Uchida Y., Wascko M.O., Calabria N.F., Catanesi M.G., Intonti R.A., Radicioni E., De Rosa G., Ali A., Collazuol G., Iacob F., Ludovici L., Cao S., Friend M., Hasegawa T., Ishida T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K., Hasegawa M., Isobe Y., Miyabe H., Sugimoto T., Suzuki A.T., Takeuchi Y., Ashida Y.

Physical Review D (Physical Review D) 99 ( 3 ) 2019.02

ISSN 24700010

Neutral current (NC) interactions of atmospheric neutrinos on oxygen form one of the major backgrounds in the search for supernova relic neutrinos with water-based Cherenkov detectors. The NC channel is dominated by neutrino quasielastic (NCQE) scattering off nucleons inside O16 nuclei. In this paper we report the first measurement of NCQE cross section using atmospheric neutrinos at Super-Kamiokande (SK). The measurement used 2,778 live days of SK-IV data with a fiducial volume of 22.5 kiloton water. Within the visible energy window of 7.5-29.5 MeV, we observed 117 events compared to the expected 71.9 NCQE signal and 53.1 background events. Weighted by the atmospheric neutrino spectrum from 160 MeV to 10 GeV, the flux averaged NCQE cross section is measured to be (1.01±0.17(stat.)-0.30+0.78(sys.))×10-38 cm2.

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Search for neutral-current induced single photon production at the ND280 near detector in T2K

Abe K., Akutsu R., Ali A., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Awataguchi Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz-Kwasniak M., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., Rosa G.D., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda Y., Gameil K., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haigh J.T., Hamacher-Baumann P., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hong Van N.T., Hosomi F., Ichikawa A.K., Ikeda M., Inoue T., Intonti R.A., Ishida T., Ishii T., Ishitsuka M., Iwamoto K., Izmaylov A.

Journal of Physics G: Nuclear and Particle Physics (Journal of Physics G: Nuclear and Particle Physics) 46 ( 8 ) 2019

ISSN 09543899

Neutrino neutral-current (NC) induced single photon production is a subleading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the finegrained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron positron pairs, we achieved 95% pure gamma ray sample from 5.738 1020 protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114 10-38 cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of .En. ~ 0.6 GeV. This is the first limit on this process below 1.GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.

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Search for CP Violation in Neutrino and Antineutrino Oscillations by the T2K Experiment with 2.2×1021 Protons on Target

Abe K., Akutsu R., Ali A., Amey J., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz M., Bench F., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dokania N., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Fernandez P., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fujita R., Fukuda D., Fukuda Y., Gameil K., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haegel L., Haigh J.T., Hamacher-Baumann P., Hansen D., Harada J., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiramoto A., Hogan M., Holeczek J., Hosomi F., Ichikawa A.K., Ikeda M., Imber J., Inoue T., Intonti R.A., Ishida T., Ishii T.

Physical Review Letters (Physical Review Letters) 121 ( 17 ) 2018.10

ISSN 00319007

The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×1020 protons on target in the neutrino (antineutrino) mode, 89 νe candidates and seven anti-νe candidates are observed, while 67.5 and 9.0 are expected for δCP=0 and normal mass ordering. The obtained 2σ confidence interval for the CP-violating phase, δCP, does not include the CP-conserving cases (δCP=0, π). The best-fit values of other parameters are sin2θ23=0.526-0.036+0.032 and Δm322=2.463-0.070+0.071×10-3 eV2/c4.

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Measurement of the tau neutrino cross section in atmospheric neutrino oscillations with Super-Kamiokande

Li Z., Abe K., Bronner C., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Nakahata M., Nakajima Y., Nakano Y., Nakayama S., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Tasaka S., Tomura T., Akutsu R., Kajita T., Nishimura Y., Okumura K., Tsui K.M., Fernandez P., Labarga L., Blaszczyk F.D.M., Gustafson J., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Berkman S., Tobayama S., Elnimr M., Kropp W.R., Locke S., Mine S., Weatherly P., Smy M.B., Sobel H.W., Takhistov V., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Himmel A., O'Sullivan E., Scholberg K., Walter C.W., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Smith S.N., Amey J., Litchfield R.P., Ma W.Y., Uchida Y., Wascko M.O., Cao S., Friend M., Hasegawa T., Ishida T., Ishii T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K., Hasegawa M., Suzuki A.T., Takeuchi Y., Yano T., Hayashino T., Hiraki T., Hirota S., Huang K., Jiang M., Mori M., Nakamura K.E., Nakaya T., Patel N.D., Wendell R.A., Anthony L.H.V., McCauley N.

Physical Review D (Physical Review D) 98 ( 5 ) 2018.09

ISSN 24700010

Using 5326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47±0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau appearance with a significance level of 4.6σ. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be (0.94±0.20)×10-38 cm2. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5σ.

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Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K

Abe K., Amey J., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz M., Berardi V., Berkman S., Berner R.M., Berns L., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bordoni S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fukuda D., Fukuda Y., Garcia A., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haegel L., Haigh J.T., Hamacher-Baumann P., Hansen D., Harada J., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiraki T., Hiramoto A., Hirota S., Hogan M., Holeczek J., Hosomi F., Ichikawa A.K., Ikeda M., Imber J., Inoue T., Intonti R.A., Ishida T., Ishii T., Iwamoto K., Izmaylov A., Jamieson B.

Physical Review D (Physical Review D) 98 ( 3 ) 2018.08

ISSN 24700010

This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×1020 protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state, the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.

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Measurement of inclusive double-differential νμ charged-current cross section with improved acceptance in the T2K off-axis near detector

Abe K., Amey J., Andreopoulos C., Anthony L., Antonova M., Aoki S., Ariga A., Ashida Y., Azuma Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz M., Berardi V., Berkman S., Berner R.M., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bordoni S., Bourguille B., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calcutt J., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Feusels T., Finch A.J., Fiorentini G.A., Fiorillo G., Francois C., Friend M., Fujii Y., Fukuda D., Fukuda Y., Garcia A., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haegel L., Haigh J.T., Hamacher-Baumann P., Hansen D., Harada J., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hiraki T., Hiramoto A., Hirota S., Hogan M., Holeczek J., Hosomi F., Ichikawa A.K., Ikeda M., Imber J., Inoue T., Intonti R.A., Ishida T., Ishii T., Iwamoto K., Izmaylov A., Jamieson B., Jiang M.

Physical Review D (Physical Review D) 98 ( 1 ) 2018.07

ISSN 24700010

We report a measurement of the flux-integrated cross section for inclusive muon neutrino charged-current interactions on carbon. The double-differential measurements are given as a function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here corresponds to 5.7×1020 protons on target. The total flux-integrated cross section is measured to be (6.950±0.662)×10-39 cm2 nucleon-1 and is consistent with our simulation.

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Physics potentials with the second Hyper-Kamiokande detector in Korea

Abe K., Abe K., Ahn S.H., Aihara H., Aimi A., Akutsu R., Andreopoulos C., Anghel I., Anthony L.H.V., Antonova M., Ashida Y., Aushev V., Barbi M., Barker G.J., Barr G., Beltrame P., Berardi V., Bergevin M., Berkman S., Berns L., Berry T., Bhadra S., Blaszczyk F.D.M., Blondel A., Bolognesi S., Boyd S.B., Bravar A., Bronner C., Buizza Avanzini M., Cafagna F.S., Calland R., Cao S., Cartwright S.L., Catanesi M.G., Checchia C., Chen-Wishart Z., Cheon B.G., Cheoun M.K., Cho K., Choi J.H., Choi K., Choi K.Y., Chun E.J., Cole A., Coleman J., Collazuol G., Cowan G., Cremonesi L., Dealtry T., De Rosa G., Densham C., Dewhurst D., Drakopoulou E., Di Lodovico F., Drapier O., Dumarchez J., Dunne P., Dziewiecki M., Emery S., Esmaili A., Evangelisti A., Fernández-Martinez E., Feusels T., Finch A., Fiorentini G.A., Fiorillo G., Fitton M., Frankiewicz K., Friend M., Fujii Y., Fukuda Y., Fukuda D., Ganezer K., Ghosh M., Giganti C., Gonin M., Grant N., Gumplinger P., Hadley D.R., Hartfiel B., Hartz M., Hayato Y., Hayrapetyan K., Hill J., Hirota S., Horiuchi S., Ichikawa A.K., Iijima T., Ikeda M., Imber J., Inoue K., Insler J., Intonti R.A., Ioannisian A., Ishida T., Ishino H., Ishitsuka M., Itow Y., Iwamoto K., Izmaylov A.

Progress of Theoretical and Experimental Physics (Progress of Theoretical and Experimental Physics) 2018 ( 6 ) 2018.06

Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520 kt, with the first one in Japan at 295 km from the J-PARC neutrino beam with 2.5° off-axis angles (OAAs), and the second one possibly in Korea at a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics, mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1000-1300 km and OAAs of 1°-3°. We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD × 2) or Korea (JD + KD), and compared the results with a single detector in Japan. Leptonic charge-parity (CP) symmetry violation sensitivity is improved, especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1088 km baseline, 1.3° OAA). Thanks to a larger (1000 m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.

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Search for Boosted Dark Matter Interacting with Electrons in Super-Kamiokande

Kachulis C., Abe K., Bronner C., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Nakahata M., Nakano Y., Nakayama S., Okajima Y., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Tasaka S., Tomura T., Akutsu R., Kajita T., Kaneyuki K., Nishimura Y., Okumura K., Tsui K.M., Labarga L., Fernandez P., Blaszczyk F.D.M., Gustafson J., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Berkman S., Tobayama S., Goldhaber M., Elnimr M., Kropp W.R., Mine S., Locke S., Weatherly P., Smy M.B., Sobel H.W., Takhistov V., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Himmel A., Li Z., O'Sullivan E., Scholberg K., Walter C.W., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Smith S.N., Amey J., Litchfield R.P., Ma W.Y., Uchida Y., Wascko M.O., Cao S., Friend M., Hasegawa T., Ishida T., Ishii T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K., Hasegawa M., Suzuki A.T., Takeuchi Y., Yano T., Hayashino T., Hiraki T., Hirota S., Huang K., Jiang M., Nakamura K., Nakaya T., Quilain B., Patel N.D., Wendell R.A.

Physical Review Letters (Physical Review Letters) 120 ( 22 ) 2018.05

ISSN 00319007

A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.

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Search for Neutrinos in Super-Kamiokande Associated with the GW170817 Neutron-star Merger

Abe K., Bronner C., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Nakahata M., Nakajima Y., Nakano Y., Nakayama S., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Tasaka S., Yano T., Akutsu R., Kajita T., Nishimura Y., Okumura K., Tsui K.M., Labarga L., Fernandez P., Blaszczyk F.D.M., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Berkman S., Tobayama S., Bian J., Elnimr M., Kropp W.R., Locke S., Mine S., Weatherly P., Smy M.B., Sobel H.W., Takhistov V., Ganezer K.S., Hill J., Kim J.Y., Lim I.T., Park R.G., Li Z., O'Sullivan E., Scholberg K., Walter C.W., Gonin M., Imber J., Mueller T.A., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Amey J., Litchfield R.P., Ma W.Y., Uchida Y., Wascko M.O., Catanesi M.G., Intonti R.A., Radicioni E., Rosa G.D., Ali A., Collazuol G., Ludovici L., Cao S., Friend M., Hasegawa T., Ishida T., Ishii T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K.E., Hasegawa M., Suzuki A.T., Takeuchi Y., Hayashino T., Hirota S., Jiang M., Mori M., Nakamura K.E.

Astrophysical Journal Letters (Astrophysical Journal Letters) 857 ( 1 ) 2018.04

ISSN 20418205

We report the results of a neutrino search in Super-Kamiokande (SK) for coincident signals with the first detected gravitational wave (GW) produced by a binary neutron-star merger, GW170817, which was followed by a short gamma-ray burst, GRB170817A, and a kilonova/macronova. We searched for coincident neutrino events in the range from 3.5 MeV to ∼100 PeV, in a time window ±500 s around the gravitational wave detection time, as well as during a 14-day period after the detection. No significant neutrino signal was observed for either time window. We calculated 90% confidence level upper limits on the neutrino fluence for GW170817. From the upward-going-muon events in the energy region above 1.6 GeV, the neutrino fluence limit is () cm-2 for muon neutrinos (muon antineutrinos), with an error range of ±5around the zenith angle of NGC4993, and the energy spectrum is under the assumption of an index of-2. The fluence limit for neutrino energies less than 100 MeV, for which the emission mechanism would be different than for higher-energy neutrinos, is also calculated. It is 6.6 × 107 cm-2 for anti-electron neutrinos under the assumption of a Fermi-Dirac spectrum with average energy of 20 MeV.

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Atmospheric neutrino oscillation analysis with external constraints in Super-Kamiokande I-IV

Abe K., Bronner C., Haga Y., Hayato Y., Ikeda M., Iyogi K., Kameda J., Kato Y., Kishimoto Y., Marti L., Miura M., Moriyama S., Nakahata M., Nakajima T., Nakano Y., Nakayama S., Okajima Y., Orii A., Pronost G., Sekiya H., Shiozawa M., Sonoda Y., Takeda A., Takenaka A., Tanaka H., Tasaka S., Tomura T., Akutsu R., Irvine T., Kajita T., Kametani I., Kaneyuki K., Nishimura Y., Okumura K., Richard E., Tsui K.M., Labarga L., Fernandez P., Blaszczyk F.D.M., Gustafson J., Kachulis C., Kearns E., Raaf J.L., Stone J.L., Sulak L.R., Berkman S., Tobayama S., Goldhaber M., Carminati G., Elnimr M., Kropp W.R., Mine S., Locke S., Renshaw A., Smy M.B., Sobel H.W., Takhistov V., Weatherly P., Ganezer K.S., Hartfiel B.L., Hill J., Hong N., Kim J.Y., Lim I.T., Park R.G., Akiri T., Himmel A., Li Z., O'Sullivan E., Scholberg K., Walter C.W., Wongjirad T., Ishizuka T., Nakamura T., Jang J.S., Choi K., Learned J.G., Matsuno S., Smith S.N., Amey J., Litchfield R.P., Ma W.Y., Uchida Y., Wascko M.O., Cao S., Friend M., Hasegawa T., Ishida T., Ishii T., Kobayashi T., Nakadaira T., Nakamura K., Oyama Y., Sakashita K., Sekiguchi T., Tsukamoto T., Abe K., Hasegawa M., Suzuki A.T., Takeuchi Y.

Physical Review D (Physical Review D) 97 ( 7 ) 2018.04

ISSN 24700010

An analysis of atmospheric neutrino data from all four run periods of Super-Kamiokande optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for Δm322, sin2θ23, sin2θ13 and δCP are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses, based on atmospheric neutrino data alone. Additional constraints from reactor data on θ13 and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.9% and 94.5% based on the combined Super-Kamiokande plus T2K result.

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Measurement of the single π 0 production rate in neutral current neutrino interactions on water

Abe K., Amey J., Andreopoulos C., Antonova M., Aoki S., Ariga A., Ashida Y., Assylbekov S., Autiero D., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Bartet-Friburg P., Batkiewicz M., Berardi V., Berkman S., Bhadra S., BienstocK S., Blondel A., Bolognesi S., Bordoni S., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calland R.G., Campbell T., Cao S., Cartwright S.L., Castillo R., Catanesi M.G., Cervera A., Chappell A., Checchia C., CherdacK D., Chikuma N., Christodoulou G., Clifton A., Coleman J., Collazuol G., Coplowe D., Cremonesi L., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Dewhurst D., Di Lodovico F., Di Luise S., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunkman M., Dunne P., Dziewiecki M., Emery-SchrenK S., Ereditato A., Feusels T., Finch A.J., Fiorentini G.A., Friend M., Fujii Y., Fukuda D., Fukuda Y., Furmanski A.P., Galymov V., Garcia A., Giffin S.G., Giganti C., Gilje K., Gizzarelli F., Golan T., Gonin M., Grant N., Hadley D.R., Haegel L., Haigh J.T., Hamilton P., Hansen D., Harada J., Hara T., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Helmer R.L., Hierholzer M., Hillairet A., Himmel A., Hiraki T., Hiramoto A., Hirota S.

Physical Review D (Physical Review D) 97 ( 3 ) 2018.02

ISSN 24700010

The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the PØD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the PØD contained water (2.64×1020 protons-on-target) and also periods without water (3.49×1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106±41±69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68±0.26(stat)±0.44(sys)±0.12(flux). The nominal simulation uses a flux integrated cross section of 7.63×10-39 cm2 per nucleon with an average neutrino interaction energy of 1.3 GeV.

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First measurement of the νμ charged-current cross section on a water target without pions in the final state

Abe K., Amey J., Andreopoulos C., Antonova M., Aoki S., Ariga A., Ashida Y., Ban S., Barbi M., Barker G.J., Barr G., Barry C., Batkiewicz M., Berardi V., Berkman S., Bhadra S., Bienstock S., Blondel A., Bolognesi S., Bordoni S., Boyd S.B., Brailsford D., Bravar A., Bronner C., Buizza Avanzini M., Calland R.G., Campbell T., Cao S., Cartwright S.L., Catanesi M.G., Cervera A., Chappell A., Checchia C., Cherdack D., Chikuma N., Christodoulou G., Coleman J., Collazuol G., Coplowe D., Cudd A., Dabrowska A., De Rosa G., Dealtry T., Denner P.F., Dennis S.R., Densham C., Di Lodovico F., Dolan S., Drapier O., Duffy K.E., Dumarchez J., Dunne P., Emery-Schrenk S., Ereditato A., Feusels T., Finch A.J., Fiorentini G.A., Friend M., Fujii Y., Fukuda D., Fukuda Y., Garcia A., Giganti C., Gizzarelli F., Golan T., Gonin M., Hadley D.R., Haegel L., Haigh J.T., Hansen D., Harada J., Hartz M., Hasegawa T., Hastings N.C., Hayashino T., Hayato Y., Hillairet A., Hiraki T., Hiramoto A., Hirota S., Hogan M., Holeczek J., Hosomi F., Huang K., Ichikawa A.K., Ikeda M., Imber J., Insler J., Intonti R.A., Ishida T., Ishii T., Iwai E., Iwamoto K., Izmaylov A., Jamieson B., Jiang M., Johnson S., Jonsson P., Jung C.K., Kabirnezhad M.

Physical Review D (Physical Review D) 97 ( 1 ) 2018.01

ISSN 24700010

This paper reports the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment's off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be σ=(0.95±0.08(stat)±0.06(det syst)±0.04(model syst)±0.08(flux))×10-38 cm2/n.

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