Details of a Researcher - NISHIMURA Yasuhiro

Papers - NISHIMURA Yasuhiro

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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.

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