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Search for proton decay into a single charged antilepton and a massless invisible particle using the full pure water data set of Super-Kamiokande

Y. M. Liu ²⁵, K. Terada⁵², K. Abe^1,51, Y. Asaoka^1,51, M. Harada¹, Y. Hayato^1,51, K. Hiraide^1,51, T. H. Hung¹, K. Ieki^1,51 et al. (Super-Kamiokande Collaboration)

K. Ieki^1,51, M. Ikeda^1,51, J. Kameda^1,51, Y. Kataoka^1,51, S. Mine^1,7, M. Miura^1,51, S. Moriyama^1,51, K. Nakagiri¹, M. Nakahata^1,51, S. Nakayama^1,51, Y. Noguchi¹, G. Pronost¹, K. Sato¹, H. Sekiya^1,51, R. Shinoda¹, M. Shiozawa^1,51, Y. Suzuki¹, A. Takeda^1,51, Y. Takemoto^1,51, H. Tanaka^1,51, S. Chen², Y. Itow^2,33,34, T. Kajita^2,51,24, R. Nishijima², K. Okumura^2,51, T. Tashiro², T. Tomiya², X. Wang², F. J. de Garay Arcones³, P. Fernandez³, L. Labarga³, D. Samudio³, C. Yanagisawa^4,38, B. Jargowsky⁵, E. Kearns^5,51, J. Mirabito⁵, L. Wan⁵, T. Wester⁵, B. W. Pointon^6,55, J. Bian⁷, B. Cortez⁷, N. J. Griskevich⁷, Y. Jiang⁷, M. B. Smy^7,51, H. W. Sobel^7,51, V. Takhistov^7,26, J. Hill⁸, B. D. Xu⁹, D. Jung¹⁰, D. H. Moon¹⁰, R. G. Park¹⁰, B. S. Yang¹⁰, K. Scholberg^11,51, C. W. Walter^11,51, O. Drapier¹², A. Ershova¹², M. Ferey¹², Z. Hu¹², E. Le Blévec¹², T. Leplumey¹², Th. A. Mueller¹², P. Paganini¹², C. Quach¹², R. Rogly¹², T. Nakamura¹³, J. S. Jang¹⁴, R. P. Litchfield¹⁵, L. N. Machado¹⁵, F. J. P. Soler¹⁵, J. G. Learned¹⁶, K. Choi¹⁷, S. Cao¹⁸, T. V. Ngoc¹⁸, L. H. V. Anthony¹⁹, N. W. Prouse¹⁹, M. Scott¹⁹, Y. Uchida¹⁹, V. Berardi²⁰, N. F. Calabria²⁰, M. G. Catanesi²⁰, N. Ospina²⁰, E. Radicioni²⁰, A. Langella²¹, G. De Rosa²¹, G. T. Burton²², G. Collazuol²², M. Feltre²², M. Mattiazzi²², L. Ludovici²³, M. Gonin²⁴, L. Périssé²⁴, B. Quilain²⁴, M. Fukazawa²⁵, S. Horiuchi²⁵, A. Kawabata²⁵, Y. Maekawa²⁵, Y. Nishimura²⁵, A. Oka²⁵, H. Tanigawa²⁵, R. Akutsu²⁶, M. Friend²⁶, T. Hasegawa²⁶, Y. Hino²⁶, T. Ishida²⁶, T. Kobayashi²⁶, T. Matsubara²⁶, T. Nakadaira²⁶, Y. Oyama²⁶, A. Portocarrero Yrey²⁶, K. Sakashita²⁶, T. Sekiguchi²⁶, N. Bhuiyan²⁷, F. Di Lodovico²⁷, T. Katori²⁷, R. Kralik²⁷, N. Latham²⁷, R. M. Ramsden²⁷, V. Siccardi²⁷, S. Aoyama²⁸, H. Bambara²⁸, Y. Inaba²⁸, H. Ito²⁸, M. Nishigami²⁸, T. Sone²⁸, A. T. Suzuki²⁸, Y. Takeuchi^28,51, S. Wada²⁸, H. Zhong²⁸, J. Feng²⁹, L. Feng²⁹, N. Fujimoto²⁹, S. Han²⁹, J. Hikida²⁹, M. Kawaue²⁹, T. Kikawa²⁹, F. Nakanishi²⁹, T. Nakaya^29,51, R. A. Wendell^29,51, S. J. Jenkins³⁰, N. McCauley³⁰, M. Fanì³¹, M. J. Wilking³¹, Z. Xie³¹, Y. Fukuda³², H. Menjo^33,34, Y. Yoshioka³³, J. Lagoda³⁵, J. Zalipska³⁵, T. Yano³⁶, M. Mori³⁷, J. Jiang³⁸, Y. Asano³⁹, K. Hamaguchi³⁹, H. Ishino³⁹, Y. Koshio^39,51, S. Ohshita³⁹, T. Tada³⁹, T. Ishizuka⁴⁰, G. Barr⁴¹, D. Barrow⁴¹, D. Wark^41,47, A. Holin⁴², F. Nova⁴², M. Jo⁴³, S. Jung⁴³, J. Yoo⁴³, L. Kneale⁴⁴, T. Peacock⁴⁴, P. Stowell⁴⁴, H. Okazawa⁴⁵, S. M. Lakshmi⁴⁶, S. Hong⁴⁸, E. Kwon⁴⁸, M. W. Lee⁴⁸, J. W. Seo⁴⁸, I. Yu⁴⁸, Y. Ashida⁴⁹, A. K. Ichikawa⁴⁹, S. Kobayashi⁴⁹, K. D. Nakamura⁴⁹, S. Abe⁵⁰, W. Cai⁵⁰, Y. Endo⁵⁰, S. Goto⁵⁰, S. Kodama⁵⁰, Y. Kong⁵⁰, H. Hayasaki⁵⁰, Y. Masaki⁵⁰, Y. Mizuno⁵⁰, T. Muro⁵⁰, K. Nakagiri⁵⁰, Y. Nakajima^50,51, M. Sekiyama⁵⁰, N. Taniuchi⁵⁰, T. Yamazumi⁵⁰, M. Yokoyama^50,51, P. de Perio⁵¹, S. Fujita⁵¹, C. Jesús-Valls⁵¹, K. Martens⁵¹, Ll. Marti⁵¹, A. D. Santos⁵¹, K. M. Tsui⁵¹, M. R. Vagins^51,7, S. Izumiyama⁵², M. Kuze⁵², R. Matsumoto⁵², C. Ise⁵³, M. Ishitsuka⁵³, M. Sugo⁵³, M. Wako⁵³, K. Yamauchi⁵³, Y. Nakano⁵⁴, A. Yankelevich⁵⁴, F. Cormier⁵⁵, R. Gaur⁵⁵, M. Hartz⁵⁵, A. Konaka⁵⁵, X. Li⁵⁵, B. R. Smithers⁵⁵, S. Chen⁵⁶, Y. Wu⁵⁶, A. Q. Zhang⁵⁶, B. Zhang⁵⁶, H. Adhikary⁵⁷, M. Girgus⁵⁷, P. Govindaraj⁵⁷, M. Posiadala-Zezula⁵⁷, Y. S. Prabhu⁵⁷, S. B. Boyd⁵⁸, R. Edwards⁵⁸, D. Hadley⁵⁸, M. O’Flaherty⁵⁸, B. Richards⁵⁸, A. Ali^59,55, B. Jamieson⁵⁹, C. Bronner⁶⁰, D. Horiguchi⁶⁰, A. Minamino⁶⁰, and Y. Sasaki⁶⁰ (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
⁹School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 101408, China
¹⁰Institute for Universe and Elementary Particles, Chonnam National University, Gwangju 61186, Korea
¹¹Department of Physics, Duke University, Durham, North Carolina 27708, USA
¹²Ecole Polytechnique, IN2P3-CNRS, Laboratoire Leprince-Ringuet, F-91120 Palaiseau, France
¹³Department of Physics, Gifu University, Gifu City, Gifu 501-1193, Japan
¹⁴GIST College, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
¹⁵School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
¹⁶Department of Physics and Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
¹⁷Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, 34126, Korea
¹⁸Institute For Interdisciplinary Research in Science and Education, ICISE, Quy Nhon, 55121, Vietnam
¹⁹Department of Physics, Imperial College London, London, SW7 2AZ, United Kingdom
²⁰Dipartimento Interuniversitario di Fisica, INFN Sezione di Bari and Università e Politecnico di Bari, I-70125, Bari, Italy
²¹Dipartimento di Fisica, INFN Sezione di Napoli and Università di Napoli, I-80126, Napoli, Italy
²²Dipartimento di Fisica, INFN Sezione di Padova and Università di Padova, I-35131, Padova, Italy
²³INFN Sezione di Roma and Università di Roma “La Sapienza,” I-00185, Roma, Italy
²⁴ILANCE, CNRS—University of Tokyo International Research Laboratory, Kashiwa, Chiba 277-8582, Japan
²⁵Department of Physics, Keio University, Yokohama, Kanagawa, 223-8522, Japan
²⁶High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
²⁷Department of Physics, King’s College London, London, WC2R 2LS, United Kingdom
²⁸Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan
²⁹Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan
³⁰Department of Physics, University of Liverpool, Liverpool, L69 7ZE, United Kingdom
³¹School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
³²Department of Physics, Miyagi University of Education, Sendai, Miyagi 980-0845, Japan
³³Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8602, Japan
³⁴Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya, Aichi 464-8602, Japan
³⁵National Centre For Nuclear Research, 02-093 Warsaw, Poland
³⁶National Institute of Technology, Niihama College, Niihama, Ehime 792-8580, Japan
³⁷National Institute of Technology, Numazu College, Numazu, Shizuoka 410-8501, Japan
³⁸Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800, USA
³⁹Department of Physics, Okayama University, Okayama, Okayama 700-8530, Japan
⁴⁰Media Communication Center, Osaka Electro-Communication University, Neyagawa, Osaka, 572-8530, Japan
⁴¹Department of Physics, Oxford University, Oxford, OX1 3PU, United Kingdom
⁴²Rutherford Appleton Laboratory, Harwell, Oxford, OX11 0QX, United Kingdom
⁴³Department of Physics and Astronomy, Seoul National University, Seoul 151-742, Korea
⁴⁴School of Mathematical and Physical Sciences, University of Sheffield, S3 7RH, Sheffield, United Kingdom
⁴⁵Department of Informatics in Social Welfare, Shizuoka University of Welfare, Yaizu, Shizuoka, 425-8611, Japan
⁴⁶August Chełkowski Institute of Physics, University of Silesia in Katowice, 75 Pułku Piechoty 1, 41-500 Chorzów, Poland
⁴⁷STFC, Rutherford Appleton Laboratory, Harwell Oxford, and Daresbury Laboratory, Warrington, OX11 0QX, United Kingdom
⁴⁸Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
⁴⁹Department of Physics, Faculty of Science, Tohoku University, Sendai, Miyagi, 980-8578, Japan
⁵⁰Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
⁵¹Kavli 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
⁵²Department of Physics, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
⁵³Department of Physics and Astronomy, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan
⁵⁴Faculty of Science, University of Toyama, Toyama City, Toyama 930-8555, Japan
⁵⁵TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3, Canada
⁵⁶Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
⁵⁷Faculty of Physics, University of Warsaw, Warsaw, 02-093, Poland
⁵⁸Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom
⁵⁹Department of Physics, University of Winnipeg, Winnipeg, Manitoba MB R3J 3L8, Canada
⁶⁰Department of Physics, Yokohama National University, Yokohama, Kanagawa, 240-8501, Japan

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Phys. Rev. D 114, 072005 – Published 13 October, 2026

DOI: https://doi.org/10.1103/rsr5-d3x2

Abstract

A search for proton decay via $p \to l^{+} + X$ , where $l^{+}$ is a positively charged lepton and $X$ is an invisible, massless, neutral particle, was performed using a $401 kton \cdot years$ exposure representing the entire pure water phase of Super-Kamiokande. No significant indication of a proton decay was observed beyond the expected atmospheric neutrino background. Lower limits on the partial lifetime of the proton were set to $1.72 \times 10^{33} years$ for $p \to e^{+} + X$ and $0.61 \times 10^{33} years$ for $p \to μ^{+} + X$ at the 90% confidence level. These results improve on previous limits by factors of 2 and 1.5, respectively.

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Phys. Rev. D 114, 072005– Published 13 October, 2026

Vol. 114, Iss. 7 — 1 October 2026

Received 1 September 2026
Accepted 18 September 2026

DOI: https://doi.org/10.1103/rsr5-d3x2

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.

Published by the American Physical Society

Physical Review D

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Search for proton decay into a single charged antilepton and a massless invisible particle using the full pure water data set of Super-Kamiokande

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