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Neutron-Multiplicity Measurement in Muon Capture on Oxygen Nuclei in the Gadolinium-Loaded Super-Kamiokande Detector

S. Miki ¹, K. Abe ^1,50, S. Abe ¹, Y. Asaoka ^1,50, C. Bronner ¹, M. Harada ¹, Y. Hayato ^1,50, K. Hiraide ^1,50, K. Hosokawa ¹ et al. (The Super-Kamiokande Collaboration)

K. Hosokawa ¹, K. Ieki ^1,50, M. Ikeda ^1,50, J. Kameda^1,50, Y. Kanemura¹, R. Kaneshima¹, Y. Kashiwagi¹, Y. Kataoka ^1,50, S. Mine^1,8, M. Miura ^1,50, S. Moriyama ^1,50, M. Nakahata ^1,50, S. Nakayama ^1,50, Y. Noguchi ¹, K. Okamoto¹, G. Pronost ¹, K. Sato¹, H. Sekiya ^1,50, H. Shiba¹, K. Shimizu¹, M. Shiozawa ^1,50, Y. Sonoda¹, Y. Suzuki¹, A. Takeda^1,50, Y. Takemoto ^1,50, A. Takenaka¹, H. Tanaka^1,50, S. Watanabe¹, T. Yano ¹, T. Kajita^2,50,24, K. Okumura ^2,50, T. Tashiro ², T. Tomiya², X. Wang², S. Yoshida², G. D. Megias³, P. Fernandez ⁴, L. Labarga ⁴, N. Ospina ⁴, B. Zaldivar⁴, B. W. Pointon ^7,55, C. Yanagisawa ^5,36, E. Kearns ^6,50, J. L. Raaf⁶, L. Wan ⁶, T. Wester ⁶, J. Bian⁸, B. Cortez⁸, N. J. Griskevich ⁸, S. Locke⁸, M. B. Smy ^8,50, H. W. Sobel ^8,50, V. Takhistov^8,26, A. Yankelevich ⁸, J. Hill⁹, M. C. Jang¹⁰, S. H. Lee¹⁰, D. H. Moon ¹⁰, R. G. Park¹⁰, B. S. Yang ¹⁰, B. Bodur ¹¹, K. Scholberg ^11,50, C. W. Walter ^11,50, A. Beauchêne¹², O. Drapier ¹², A. Ershova ¹², A. Giampaolo¹², Th. A. Mueller ¹², A. D. Santos ¹², P. Paganini ¹², C. Quach¹², B. Quilain¹², R. Rogly ¹², T. Nakamura¹³, J. S. Jang¹⁴, R. P. Litchfield¹⁵, L. N. Machado ¹⁵, F. J. P. Soler ¹⁵, J. G. Learned¹⁶, K. Choi¹⁷, N. Iovine¹⁷, S. Cao¹⁸, L. H. V. Anthony¹⁹, D. Martin¹⁹, N. W. Prouse ¹⁹, M. Scott ¹⁹, A. A. Sztuc¹⁹, Y. Uchida¹⁹, V. Berardi ²⁰, N. F. Calabria ²⁰, M. G. Catanesi²⁰, E. Radicioni²⁰, N. F. Calabria²², A. Langella ²², G. De Rosa²¹, G. Collazuol ²², M. Feltre²², F. Iacob ²², M. Lamoureux²², M. Mattiazzi ²², L. Ludovici²³, M. Gonin²⁴, L. Périssé ²⁴, B. Quilain²⁴, C. Fujisawa²⁵, S. Horiuchi ²⁵, M. Kobayashi²⁵, Y. M. Liu²⁵, Y. Maekawa ²⁵, Y. Nishimura ²⁵, R. Okazaki²⁵, R. Akutsu²⁶, M. Friend²⁶, T. Hasegawa ²⁶, T. Ishida²⁶, T. Kobayashi²⁶, M. Jakkapu²⁶, T. Matsubara ²⁶, T. Nakadaira²⁶, K. Nakamura^26,50, Y. Oyama ²⁶, A. Portocarrero Yrey²⁶, K. Sakashita²⁶, T. Sekiguchi²⁶, T. Tsukamoto²⁶, N. Bhuiyan ²⁷, G. T. Burton ²⁷, F. Di Lodovico ²⁷, J. Gao²⁷, A. Goldsack²⁷, T. Katori ²⁷, J. Migenda ²⁷, R. M. Ramsden ²⁷, Z. Xie ²⁷, S. Zsoldos ^27,50, Y. Kotsar²⁸, H. Ozaki²⁸, A. T. Suzuki²⁸, Y. Takagi²⁸, Y. Takeuchi ^28,50, H. Zhong²⁸, J. Feng²⁹, L. Feng²⁹, S. Han ²⁹, J. R. Hu ²⁹, Z. Hu ²⁹, M. Kawaue²⁹, T. Kikawa²⁹, M. Mori²⁹, T. Nakaya ^29,50, T. V. Ngoc ²⁹, R. A. Wendell ^29,50, K. Yasutome²⁹, S. J. Jenkins ³⁰, N. McCauley ³⁰, P. Mehta³⁰, A. Tarrant ³⁰, M. J. Wilking ³¹, Y. Fukuda ³², Y. Itow ^33,34, H. Menjo ³³, K. Ninomiya³³, Y. Yoshioka³³, J. Lagoda³⁵, M. Mandal³⁵, P. Mijakowski³⁵, Y. S. Prabhu ³⁵, J. Zalipska³⁵, M. Jia³⁶, J. Jiang³⁶, C. K. Jung³⁶, W. Shi³⁶, M. J. Wilking³⁶, Y. Hino ³⁷, H. Ishino³⁷, H. Kitagawa³⁷, Y. Koshio ^37,50, F. Nakanishi ³⁷, S. Sakai ³⁷, T. Tada ³⁷, T. Tano³⁷, T. Ishizuka³⁸, G. Barr³⁹, D. Barrow ³⁹, L. Cook^39,50, S. Samani³⁹, D. Wark^39,45, A. Holin⁴⁰, F. Nova ⁴⁰, S. Jung ⁴¹, B. S. Yang⁴¹, J. Y. Yang ⁴¹, J. Yoo ⁴¹, J. E. P. Fannon⁴², L. Kneale ⁴², M. Malek⁴², J. M. McElwee⁴², T. Peacock⁴², P. Stowell⁴², M. D. Thiesse ⁴², L. F. Thompson⁴², S. T. Wilson⁴², H. Okazawa⁴³, S. M. Lakshmi⁴⁴, S. B. Kim⁴⁶, E. Kwon ⁴⁶, M. W. Lee ⁴⁶, J. W. Seo ⁴⁶, I. Yu ⁴⁶, A. K. Ichikawa ⁴⁷, K. D. Nakamura ⁴⁷, S. Tairafune ⁴⁷, K. Nishijima ⁴⁸, A. Eguchi⁴⁹, S. Goto⁴⁹, Y. Mizuno⁴⁹, T. Muro⁴⁹, K. Nakagiri ⁴⁹, Y. Nakajima ^49,50, S. Shima⁴⁹, N. Taniuchi⁴⁹, E. Watanabe⁴⁹, M. Yokoyama ^49,50, P. de Perio ⁵⁰, S. Fujita ⁵⁰, C. Jesús-Valls ⁵⁰, K. Martens ⁵⁰, Ll. Marti ⁵⁰, K. M. Tsui ⁵⁰, M. R. Vagins ^50,8, J. Xia⁵⁰, M. Kuze ⁵¹, S. Izumiyama ⁵¹, R. Matsumoto ⁵¹, K. Terada⁵¹, R. Asaka⁵², M. Ishitsuka⁵², H. Ito ⁵², T. Kinoshita⁵², Y. Ommura⁵², N. Shigeta⁵², M. Shinoki ⁵², T. Suganuma⁵², K. Yamauchi ⁵², T. Yoshida⁵², J. F. Martin⁵³, H. A. Tanaka⁵³, T. Towstego⁵³, Y. Nakano ⁵⁴, F. Cormier²⁹, R. Gaur⁵⁵, V. Gousy-Leblanc^55,*, M. Hartz⁵⁵, A. Konaka⁵⁵, X. Li⁵⁵, B. R. Smithers ⁵⁵, S. Chen ⁵⁶, Y. Wu⁵⁶, B. D. Xu ⁵⁶, A. Q. Zhang⁵⁶, B. Zhang⁵⁶, M. Girgus⁵⁷, P. Govindaraj⁵⁷, M. Posiadala-Zezula ⁵⁷, S. B. Boyd⁵⁸, R. Edwards⁵⁸, D. Hadley⁵⁸, M. Nicholson⁵⁸, M. O’Flaherty⁵⁸, B. Richards⁵⁸, A. Ali^59,55, B. Jamieson⁵⁹, S. Amanai⁶⁰, A. Minamino ⁶⁰, G. Pintaudi⁶⁰, S. Sano⁶⁰, R. Shibayama⁶⁰, R. Shimamura⁶⁰, S. Suzuki⁶⁰, and K. Wada⁶⁰ (The 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
³Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
⁴Department of Theoretical Physics, University Autonoma Madrid, 28049 Madrid, Spain
⁵Science Department, Borough of Manhattan Community College / City University of New York, New York, New York 1007, USA
⁶Department of Physics, Boston University, Boston, Massachusetts 02215, USA
⁷Department of Physics, British Columbia Institute of Technology, Burnaby, British Columbia V5G 3H2, Canada
⁸Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697-4575, USA
⁹Department of Physics, California State University, Dominguez Hills, Carson, California 90747, USA
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, 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, Scotland 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
³⁶Department of Physics and Astronomy, State University of New York at Stony Brook, 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, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
⁴⁹Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
⁵⁰Kavli 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
⁵¹Department of Physics, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
⁵²Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan
⁵³Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
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 R3J 3L8, Canada
⁶⁰Department 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. Lett. 136, 131801 – Published 31 March, 2026

DOI: https://doi.org/10.1103/pmyx-jn3s

Abstract

In recent neutrino detectors, neutrons produced in neutrino reactions play an important role. Muon capture on oxygen nuclei is one of the processes that produce neutrons in water Cherenkov detectors. We measured neutron multiplicity in the process using cosmic ray muons that stop in the gadolinium-loaded Super-Kamiokande detector. For this measurement, neutron detection efficiency is obtained with the muon capture events followed by gamma rays to be ${50.2}_{- 2.1}^{+ 2.0} %$ . By fitting the observed multiplicity considering the detection efficiency, we measure neutron multiplicity in muon capture as $P (0) = 24 \pm 3 %$ , $P (1) = 7 0_{- 2}^{+ 3} %$ , $P (2) = 6.1 \pm 0.5 %$ , $P (3) = 0.38 \pm 0.09 %$ . This is the first measurement of the multiplicity of neutrons associated with muon capture on oxygen without neutron energy threshold.

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References (27)

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Phys. Rev. Lett. 136, 131801– Published 31 March, 2026

Vol. 136, Iss. 13 — 3 April 2026

Received 26 March 2025
Revised 3 December 2025
Accepted 29 January 2026

DOI: https://doi.org/10.1103/pmyx-jn3s

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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Neutron-Multiplicity Measurement in Muon Capture on Oxygen Nuclei in the Gadolinium-Loaded Super-Kamiokande Detector

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