Search for Diffuse Supernova Neutrino Background with 956.2 days of Super-Kamiokande gadolinium dataset

Abstract

We report the search result for the Diffuse Supernova Neutrino Background (DSNB) in neutrino energies beyond 9.3 MeV in the gadolinium-loaded Super-Kamiokande (SK) detector with a 22,500 × 956.2 m3 day exposure. Starting in the summer of 2020, SK introduced 0.01% gadolinium (Gd) by mass into its ultrapure water to enhance the neutron capture signal, termed the SK-VI phase. This was followed by a 0.03% Gd-loading in 2022, a phase referred to as SK-VII. We then conducted a DSNB search using 552.2 days of SK-VI data and 404.0 days of SK-VII data through 2023 September. This analysis includes several new features, such as two new machine learning neutron detection algorithms with Gd, an improved atmospheric background-reduction technique, and two parallel statistical approaches. No significant excess over background predictions was found in a DSNB spectrum-independent analysis, and 90% confidence level (C.L.) upper limits on the astrophysical electron antineutrino flux were set. Additionally, a spectral fitting result exhibited a ∼1.2σ disagreement with a null DSNB hypothesis, comparable to a previous result from 5823 days of all SK pure-water phases.

Metadata

Item Type:	Article
Authors/Creators:	Abe, K. Abe, S. https://orcid.org/0000-0002-2110-5130 Asaoka, Y. https://orcid.org/0000-0001-6440-933X Harada, M. https://orcid.org/0000-0003-3273-946X Hayato, Y. https://orcid.org/0000-0002-8683-5038 Hiraide, K. https://orcid.org/0000-0003-1229-9452 Hosokawa, K. https://orcid.org/0000-0002-8766-3629 Hung, T.H. Ieki, K. https://orcid.org/0000-0002-7791-5044 Ikeda, M. https://orcid.org/0000-0002-4177-5828 Kameda, J. Kanemura, Y. Kataoka, Y. https://orcid.org/0000-0001-9090-4801 Miki, S. https://orcid.org/0009-0002-4111-5720 Mine, S. Miura, M. Moriyama, S. https://orcid.org/0000-0001-7630-2839 Nakahata, M. https://orcid.org/0000-0001-7783-9080 Nakayama, S. https://orcid.org/0000-0002-9145-714X Noguchi, Y. https://orcid.org/0000-0002-3113-3127 Pronost, G. https://orcid.org/0000-0001-6429-5387 Sato, K. Sekiya, H. https://orcid.org/0000-0001-9034-0436 Shinoda, R. Shiozawa, M. https://orcid.org/0000-0003-0520-3520 Suzuki, Y. Takeda, A. Takemoto, Y. https://orcid.org/0000-0003-2232-7277 Tanaka, H. Yano, T. https://orcid.org/0000-0002-5320-1709 Itow, Y. https://orcid.org/0000-0002-8198-1968 Kajita, T. Nishijima, R. Okumura, K. https://orcid.org/0000-0002-5523-2808 Tashiro, T. https://orcid.org/0000-0003-1440-3049 Tomiya, T. Wang, X. Fernandez, P. https://orcid.org/0000-0001-9034-1930 Labarga, L. https://orcid.org/0000-0002-6395-9142 Samudio, D. https://orcid.org/0009-0004-7780-7571 Zaldivar, B. Yanagisawa, C. https://orcid.org/0000-0002-6490-1743 Kearns, E. https://orcid.org/0000-0002-1781-150X Mirabito, J. Wan, L. https://orcid.org/0000-0001-5524-6137 Wester, T. https://orcid.org/0000-0001-6668-7595 Pointon, B.W. https://orcid.org/0000-0003-0312-4044 Bian, J. Cortez, B. Griskevich, N.J. https://orcid.org/0000-0003-4409-3184 Jiang, Y. Smy, M.B. Sobel, H.W. https://orcid.org/0000-0001-5073-4043 Takhistov, V. Yankelevich, A. https://orcid.org/0000-0002-5963-3123 Hill, J. Jang, M.C. Lee, S.H. Moon, D.H. Park, R.G. Yang, B.S. https://orcid.org/0000-0001-5877-6096 Bodur, B. https://orcid.org/0000-0001-8454-271X Scholberg, K. https://orcid.org/0000-0002-7007-2021 Walter, C.W. https://orcid.org/0000-0003-2035-2380 Beauchêne, A. https://orcid.org/0000-0001-7781-1483 Le Blévec, E. Drapier, O. Ershova, A. https://orcid.org/0000-0001-6335-2343 Ferey, M. Mueller, T.A. https://orcid.org/0000-0003-2743-4741 Santos, A.D. https://orcid.org/0000-0002-4856-4986 Paganini, P. https://orcid.org/0000-0001-9580-683X Quach, C. Rogly, R. https://orcid.org/0000-0003-2530-5217 Nakamura, T. Jang, J.S. Litchfield, R.P. Machado, L.N. https://orcid.org/0000-0002-7578-4183 Soler, F.J.P. https://orcid.org/0000-0002-4893-3729 Learned, J.G. Choi, K. Cao, S. Anthony, L.H.V. Prouse, N.W. https://orcid.org/0000-0003-1037-3081 Scott, M. https://orcid.org/0000-0002-1759-4453 Uchida, Y. Berardi, V. https://orcid.org/0000-0002-8387-4568 Calabria, N.F. https://orcid.org/0000-0003-3590-2808 Catanesi, M.G. 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Ramsden, R.M. https://orcid.org/0009-0005-3298-6593 Ito, H. https://orcid.org/0000-0003-1029-5730 Sone, T. Suzuki, A.T. Takeuchi, Y. https://orcid.org/0000-0002-4665-2210 Wada, S. Zhong, H. Feng, J. Feng, L. Han, S. https://orcid.org/0009-0002-8908-6922 Hikida, J. Hu, J.R. https://orcid.org/0000-0003-2149-9691 Hu, Z. https://orcid.org/0000-0002-0353-8792 Kawaue, M. Kikawa, T. Nakaya, T. https://orcid.org/0000-0003-3040-4674 Ngoc, T.V. https://orcid.org/0000-0002-6737-2955 Wendell, R.A. https://orcid.org/0000-0002-0969-4681 Jenkins, S.J. https://orcid.org/0000-0002-0982-8141 McCauley, N. https://orcid.org/0000-0002-5982-5125 Tarrant, A. https://orcid.org/0000-0002-8750-4759 Fanì, M. https://orcid.org/0000-0002-4284-9614 Wilking, M.J. Xie, Z. https://orcid.org/0009-0003-0144-2871 Fukuda, Y. https://orcid.org/0000-0003-2660-1958 Menjo, H. https://orcid.org/0000-0001-8466-1938 Yoshioka, Y. Lagoda, J. Mandal, M. Zalipska, J. Mori, M. Jiang, J. Hamaguchi, K. Ishino, H. 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Smithers, B.R. https://orcid.org/0000-0003-1273-985X Chen, S. https://orcid.org/0000-0002-2376-8413 Wu, Y. Xu, B.D. https://orcid.org/0000-0001-5135-1319 Zhang, A.Q. Zhang, B. Adhikary, H. Girgus, M. Govindaraj, P. Posiadala-Zezula, M. https://orcid.org/0000-0002-5154-5348 Prabhu, Y.S. Boyd, S.B. Edwards, R. Hadley, D. Nicholson, M. O’Flaherty, M. Richards, B. Ali, A. Jamieson, B. Bronner, C. https://orcid.org/0000-0001-9555-6033 Horiguchi, D. Minamino, A. https://orcid.org/0000-0001-6510-7106 Sasaki, Y. Shibayama, R. Shimamura, R.
Copyright, Publisher and Additional Information:	© 2026 The Authors. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Dates:	Accepted: 10 April 2026 Published (online): 29 June 2026 Published: 29 June 2026
Institution:	The University of Sheffield
Academic Units:	The University of Sheffield > Faculty of Science (Sheffield) > Department of Physics and Astronomy (Sheffield)
Date Deposited:	06 Jul 2026 09:35
Last Modified:	06 Jul 2026 09:35
Published Version:	https://doi.org/10.3847/1538-4357/ae6c20
Status:	Published
Publisher:	American Astronomical Society
Refereed:	Yes
Identification Number:	10.3847/1538-4357/ae6c20
Open Archives Initiative ID (OAI ID):	oai:eprints.whiterose.ac.uk:242909

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Search for Diffuse Supernova Neutrino Background with 956.2 days of Super-Kamiokande gadolinium dataset

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