Details of a Researcher - NISHIMURA Yasuhiro

Papers - NISHIMURA Yasuhiro

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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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