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Search for neutron decay into an antineutrino and a neutral kaon in 0.401 megaton-years exposure of Super-Kamiokande

K. Yamauchi ⁵¹, K. Abe^1,49, S. Abe¹, Y. Asaoka^1,49, M. Harada¹, Y. Hayato^1,49, K. Hiraide^1,49, K. Hosokawa¹, K. Ieki^1,49 et al. (Super-Kamiokande Collaboration)

K. Ieki^1,49, M. Ikeda^1,49, J. Kameda^1,49, Y. Kanemura¹, Y. Kataoka^1,49, S. Miki¹, S. Mine^1,7, M. Miura^1,49, S. Moriyama^1,49, M. Nakahata^1,49, S. Nakayama^1,49, Y. Noguchi¹, G. Pronost¹, K. Sato¹, H. Sekiya^1,49, K. Shimizu¹, R. Shinoda¹, M. Shiozawa^1,49, Y. Suzuki¹, A. Takeda^1,49, Y. Takemoto^1,49, H. Tanaka^1,49, T. Yano¹, Y. Itow^2,32,33, T. Kajita^2,49,23, R. Nishijima², K. Okumura^2,49, T. Tashiro², T. Tomiya², X. Wang², P. Fernandez³, L. Labarga³, D. Samudio³, B. Zaldivar³, B. W. Pointon^6,53, C. Yanagisawa^4,36, E. Kearns^5,49, J. Mirabito⁵, L. Wan⁵, T. Wester⁵, J. Bian⁷, B. Cortez⁷, N. J. Griskevich⁷, Y. Jiang⁷, M. B. Smy^7,49, H. W. Sobel^7,49, V. Takhistov^7,25, A. Yankelevich⁷, J. Hill⁸, M. C. Jang⁹, S. H. Lee⁹, D. H. Moon⁹, R. G. Park⁹, B. S. Yang⁹, B. Bodur¹⁰, K. Scholberg^10,49, C. W. Walter^10,49, A. Beauchêne¹¹, O. Drapier¹¹, A. Ershova¹¹, Th. A. Mueller¹¹, A. D. Santos¹¹, P. Paganini¹¹, C. Quach¹¹, R. Rogly¹¹, T. Nakamura¹², J. S. Jang¹³, R. P. Litchfield¹⁴, L. N. Machado¹⁴, F. J. P. Soler¹⁴, J. G. Learned¹⁵, K. Choi¹⁶, N. Iovine¹⁶, D. Tiwari¹⁶, S. Cao¹⁷, L. H. V. Anthony¹⁸, D. Martin¹⁸, N. W. Prouse¹⁸, M. Scott¹⁸, Y. Uchida¹⁸, V. Berardi¹⁹, N. F. Calabria¹⁹, M. G. Catanesi¹⁹, N. Ospina¹⁹, E. Radicioni¹⁹, A. Langella²⁰, G. De Rosa²⁰, G. Collazuol²¹, M. Feltre²¹, M. Mattiazzi²¹, L. Ludovici²², M. Gonin²³, L. Périssé²³, B. Quilain²³, S. Horiuchi²⁴, A. Kawabata²⁴, M. Kobayashi²⁴, Y. M. Liu²⁴, Y. Maekawa²⁴, Y. Nishimura²⁴, R. Okazaki²⁴, R. Akutsu²⁵, M. Friend²⁵, T. Hasegawa²⁵, Y. Hino²⁵, T. Ishida²⁵, T. Kobayashi²⁵, M. Jakkapu²⁵, T. Matsubara²⁵, T. Nakadaira²⁵, K. Nakamura^25,49, Y. Oyama²⁵, A. Portocarrero Yrey²⁵, K. Sakashita²⁵, T. Sekiguchi²⁵, T. Tsukamoto²⁵, N. Bhuiyan²⁶, G. T. Burton²⁶, F. Di Lodovico²⁶, J. Gao²⁶, T. Katori²⁶, R. Kralik²⁶, J. Migenda²⁶, R. M. Ramsden²⁶, S. Zsoldos^26,49, H. Ito²⁷, T. Sone²⁷, A. T. Suzuki²⁷, Y. Takagi²⁷, Y. Takeuchi^27,49, S. Wada²⁷, H. Zhong²⁷, J. Feng²⁸, L. Feng²⁸, S. Han²⁸, J. Hikida²⁸, J. R. Hu²⁸, Z. Hu²⁸, M. Kawaue²⁸, T. Kikawa²⁸, T. Nakaya^28,49, T. V. Ngoc²⁸, R. A. Wendell^28,49, K. Yasutome²⁸, S. J. Jenkins²⁹, N. McCauley²⁹, A. Tarrant²⁹, M. Fanì³⁰, M. J. Wilking³⁰, Z. Xie³⁰, Y. Fukuda³¹, H. Menjo^32,33, Y. Yoshioka³², J. Lagoda³⁴, M. Mandal³⁴, J. Zalipska³⁴, M. Mori³⁵, M. Jia³⁶, J. Jiang³⁶, W. Shi³⁶, K. Hamaguchi³⁷, H. Ishino³⁷, Y. Koshio^37,49, F. Nakanishi³⁷, S. Sakai³⁷, T. Tada³⁷, T. Tano³⁷, T. Ishizuka³⁸, G. Barr³⁹, D. Barrow³⁹, L. Cook^39,49, S. Samani³⁹, D. Wark^39,45, A. Holin⁴⁰, F. Nova⁴⁰, S. Jung⁴¹, J. Y. Yang⁴¹, J. Yoo⁴¹, J. E. P. Fannon⁴², L. Kneale⁴², M. Malek⁴², J. M. McElwee⁴², T. Peacock⁴², P. Stowell⁴², M. D. Thiesse⁴², L. F. Thompson⁴², S. T. Wilson⁴², H. Okazawa⁴³, S. M. Lakshmi⁴⁴, E. Kwon⁴⁶, M. W. Lee⁴⁶, J. W. Seo⁴⁶, I. Yu⁴⁶, A. K. Ichikawa⁴⁷, K. D. Nakamura⁴⁷, S. Tairafune⁴⁷, A. Eguchi⁴⁸, S. Goto⁴⁸, S. Kodama⁴⁸, Y. Mizuno⁴⁸, T. Muro⁴⁸, K. Nakagiri⁴⁸, Y. Nakajima^48,49, N. Taniuchi⁴⁸, E. Watanabe⁴⁸, M. Yokoyama^48,49, P. de Perio⁴⁹, S. Fujita⁴⁹, C. Jesús-Valls⁴⁹, K. Martens⁴⁹, Ll. Marti⁴⁹, K. M. Tsui⁴⁹, M. R. Vagins^49,7, J. Xia⁴⁹, S. Izumiyama⁵⁰, M. Kuze⁵⁰, R. Matsumoto⁵⁰, K. Terada⁵⁰, R. Asaka⁵¹, M. Ishitsuka⁵¹, M. Shinoki⁵¹, M. Sugo⁵¹, M. Wako⁵¹, T. Yoshida⁵¹, Y. Nakano⁵², F. Cormier⁵³, R. Gaur⁵³, V. Gousy-Leblanc^53,*, M. Hartz⁵³, A. Konaka⁵³, X. Li⁵³, B. R. Smithers⁵³, S. Chen⁵⁴, Y. Wu⁵⁴, B. D. Xu⁵⁴, A. Q. Zhang⁵⁴, B. Zhang⁵⁴, M. Girgus⁵⁵, P. Govindaraj⁵⁵, M. Posiadala-Zezula⁵⁵, Y. S. Prabhu⁵⁵, S. B. Boyd⁵⁶, R. Edwards⁵⁶, D. Hadley⁵⁶, M. Nicholson⁵⁶, M. O’Flaherty⁵⁶, B. Richards⁵⁶, A. Ali^57,53, B. Jamieson⁵⁷, S. Amanai⁵⁸, C. Bronner⁵⁸, D. Horiguchi⁵⁸, A. Minamino⁵⁸, Y. Sasaki⁵⁸, R. Shibayama⁵⁸, and R. Shimamura⁵⁸ (Super-Kamiokande Collaboration)

¹Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo, Kamioka, Gifu 506-1205, Japan
²Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
³Department of Theoretical Physics, University Autonoma Madrid, 28049 Madrid, Spain
⁴Science Department, Borough of Manhattan Community College/City University of New York, New York, New York, 1007, USA
⁵Department of Physics, Boston University, Boston, Massachusetts 02215, USA
⁶Department of Physics, British Columbia Institute of Technology, Burnaby, British Columbia, V5G 3H2, Canada
⁷Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697-4575, USA
⁸Department of Physics, California State University, Dominguez Hills, Carson, California 90747, USA
⁹Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea
¹⁰Department of Physics, Duke University, Durham North Carolina 27708, USA
¹¹Ecole Polytechnique, IN2P3-CNRS, Laboratoire Leprince-Ringuet, F-91120 Palaiseau, France
¹²Department of Physics, Gifu University, Gifu, Gifu 501-1193, Japan
¹³GIST College, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
¹⁴School of Physics and Astronomy, University of Glasgow, Glasgow, Scotland, G12 8QQ, United Kingdom
¹⁵Department of Physics and Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
¹⁶Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, 34126, Korea
¹⁷Institute For Interdisciplinary Research in Science and Education, ICISE, Quy Nhon, 55121, Vietnam
¹⁸Department of Physics, Imperial College London, London, SW7 2AZ, United Kingdom
¹⁹Dipartimento Interuniversitario di Fisica, INFN Sezione di Bari and Università e Politecnico di Bari, I-70125, Bari, Italy
²⁰Dipartimento di Fisica, INFN Sezione di Napoli and Università di Napoli, I-80126, Napoli, Italy
²¹Dipartimento di Fisica, INFN Sezione di Padova and Università di Padova, I-35131, Padova, Italy
²²INFN Sezione di Roma and Università di Roma “La Sapienza”, I-00185, Roma, Italy
²³ILANCE, CNRS-University of Tokyo International Research Laboratory, Kashiwa, Chiba 277-8582, Japan
²⁴Department of Physics, Keio University, Yokohama, Kanagawa, 223-8522, Japan
²⁵High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
²⁶Department of Physics, King’s College London, London, WC2R 2LS, United Kingdom
²⁷Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan
²⁸Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan
²⁹Department of Physics, University of Liverpool, Liverpool, L69 7ZE, United Kingdom
³⁰School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
³¹Department of Physics, Miyagi University of Education, Sendai, Miyagi 980-0845, Japan
³²Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8602, Japan
³³Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya, Aichi 464-8602, Japan
³⁴National Centre For Nuclear Research, 02-093 Warsaw, Poland
³⁵National Institute of Technology, Numazu College, Numazu, Shizuoka 410-8501, Japan
³⁶Department of Physics and Astronomy, State University of New York at Stony Brook, New York 11794-3800, USA
³⁷Department of Physics, Okayama University, Okayama, Okayama 700-8530, Japan
³⁸Media Communication Center, Osaka Electro-Communication University, Neyagawa, Osaka, 572-8530, Japan
³⁹Department of Physics, Oxford University, Oxford, OX1 3PU, United Kingdom
⁴⁰Rutherford Appleton Laboratory, Harwell, Oxford, OX11 0QX, United Kingdom
⁴¹Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea
⁴²School of Mathematical and Physical Sciences, University of Sheffield, S3 7RH, Sheffield, United Kingdom
⁴³Department of Informatics in Social Welfare, Shizuoka University of Welfare, Yaizu, Shizuoka, 425-8611, Japan
⁴⁴August Chełkowski Institute of Physics, University of Silesia in Katowice, 75 Pułku Piechoty 1, 41-500 Chorzów, Poland
⁴⁵STFC, Rutherford Appleton Laboratory, Harwell Oxford, and Daresbury Laboratory, Warrington, OX11 0QX, United Kingdom
⁴⁶Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
⁴⁷Department of Physics, Faculty of Science, Tohoku University, Sendai, Miyagi, 980-8578, Japan
⁴⁸Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
⁴⁹Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁵⁰Department of Physics, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
⁵¹Department of Physics and Astronomy, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan
⁵²Faculty of Science, University of Toyama, Toyama City, Toyama 930-8555, Japan
⁵³TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3, Canada
⁵⁴Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
⁵⁵Faculty of Physics, University of Warsaw, Warsaw, 02-093, Poland
⁵⁶Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
⁵⁷Department of Physics, University of Winnipeg, Manitoba R3J 3L8, Canada
⁵⁸Department of Physics, Yokohama National University, Yokohama, Kanagawa, 240-8501, Japan

^*Also at University of Victoria, Department of Physics and Astronomy, PO Box 1700 STN CSC, Victoria, British Columbia V8W 2Y2, Canada.

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Phys. Rev. D 112, 092004 – Published 7 November, 2025

DOI: https://doi.org/10.1103/thqt-8fp1

Abstract

We searched for bound neutron decay via $n \to \bar{ν} + K^{0}$ predicted by the grand unified theories in $0.401 Mton \cdot years$ exposure of all pure water phases in the Super-Kamiokande detector. About 4.4 times more data than in the previous search have been analyzed by a new method including a spectrum fit to kaon invariant mass distributions. No significant data excess has been observed in the signal regions. As a result of this analysis, we set a lower limit of $7.8 \times 10^{32} years$ on the neutron lifetime at a 90% confidence level.

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Phys. Rev. D 112, 092004– Published 7 November, 2025

Vol. 112, Iss. 9 — 1 November 2025

Received 1 July 2025
Accepted 15 October 2025

DOI: https://doi.org/10.1103/thqt-8fp1

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Search for neutron decay into an antineutrino and a neutral kaon in 0.401 megaton-years exposure of Super-Kamiokande

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