Search for Astrophysical Electron Antineutrinos in Super-Kamiokande with 0.01% Gadolinium-loaded Water

We report the first search result for the flux of astrophysical electron antineutrinos for energies O(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 x 552 kton center dot 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 x 2970 kton center dot day) owing to the enhanced neutron tagging. Operation with Gd increased to 0.03% started in 2022 June.

システム処理の都合により筆頭著者のみ著者登録、その他の著者については以下の通り。

K. Abe2,3, C. Bronner2 , Y. Hayato2,3 , K. Hiraide2,3 , K. Hosokawa2 , K. Ieki2,3 , M. Ikeda2,3 , J. Kameda2,3, Y. Kanemura2, R. Kaneshima2, Y. Kashiwagi2, Y. Kataoka2,3 , S. Miki2, S. Mine2,4, M. Miura2,3, S. Moriyama2,3 , Y. Nakano2 , M. Nakahata2,3 , S. Nakayama2,3 , Y. Noguchi2 , K. Okamoto2, K. Sato2, H. Sekiya2,3 , H. Shiba2, K. Shimizu2, M. Shiozawa2,3 , Y. Sonoda2, Y. Suzuki2, A. Takeda2,3, Y. Takemoto2,3 , A. Takenaka2, H. Tanaka2,3, S. Watanabe2, T. Yano2 , S. Han5, T. Kajita3,5,6, K. Okumura3,5 , T. Tashiro5 , T. Tomiya5, X. Wang5, S. Yoshida5, G. D. Megias7, P. Fernandez8 , L. Labarga8 , N. Ospina8 , B. Zaldivar8, B. W. Pointon9,10, E. Kearns3,11, J. L. Raaf11, L. Wan11 , T. Wester11 , J. Bian4, N. J. Griskevich4 , S. Locke4, M. B. Smy3,4, H. W. Sobel3,4 , V. Takhistov4,12, A. Yankelevich4 , J. Hill13, S. H. Lee14, D. H. Moon14, R. G. Park14, B. Bodur15 , K. Scholberg3,15 , C. W. Walter3,15 , A. Beauchêne16, O. Drapier16, A. Giampaolo16, Th. A. Mueller16 , A. D. Santos16, P. Paganini16 , B. Quilain16, T. Ishizuka17, T. Nakamura18, J. S. Jang19, J. G. Learned20, K. Choi21, N. Iovine21 , S. Cao22, L. H. V. Anthony23, D. Martin23, M. Scott23 , A. A. Sztuc23, Y. Uchida23, V. Berardi24 , M. G. Catanesi24, E. Radicioni24, N. F. Calabria25 , A. Langella25 , L. N. Machado25 , G. De Rosa25, G. Collazuol26 , F. Iacob26 , M. Lamoureux26, M. Mattiazzi26 , L. Ludovici27, M. Gonin6, G. Pronost6 , C. Fujisawa28, Y. Maekawa28, Y. Nishimura28 , R. Okazaki28, R. Akutsu12, M. Friend12, T. Hasegawa12 , T. Ishida12, T. Kobayashi12, M. Jakkapu12, T. Matsubara12 , T. Nakadaira12, K. Nakamura3,12, Y. Oyama12 , K. Sakashita12, T. Sekiguchi12, T. Tsukamoto12, N. Bhuiyan29, G. T. Burton29, F. Di Lodovico29 , J. Gao29, A. Goldsack29, T. Katori29 , J. Migenda29 , Z. Xie29, S. Zsoldos3,29 , Y. Kotsar30, H. Ozaki30, A. T. Suzuki30, Y. Takagi30, Y. Takeuchi3,30 , J. Feng31, L. Feng31, J. R. Hu31 , Z. Hu31 , T. Kikawa31, M. Mori31, T. Nakaya3,31 , R. A. Wendell3,31 , K. Yasutome31, S. J. Jenkins32 , N. McCauley32 , P. Mehta32, A. Tarrant32 , Y. Fukuda33 , Y. Itow34,35 , H. Menjo34 , K. Ninomiya34, J. Lagoda36, S. M. Lakshmi36, M. Mandal36, P. Mijakowski36, Y. S. Prabhu36, J. Zalipska36, M. Jia37, J. Jiang37, C. K. Jung37, M. J. Wilking37, C. Yanagisawa37,56 , Y. Hino1 , H. Ishino1, H. Kitagawa1, Y. Koshio1,3 , F. Nakanishi1 , S. Sakai1 , T. Tada1, T. Tano1, G. Barr38, D. Barrow38 , L. Cook3,38, S. Samani38, D. Wark38,39, A. Holin40, F. Nova41 , B. S. Yang40 , J. Y. Yang40 , J. Yoo40 , J. E. P. Fannon42, L. Kneale42 , M. Malek42, J. M. McElwee42, M. D. Thiesse42 , L. F. Thompson42, S. T. Wilson42, H. Okazawa43, S. B. Kim44, E. Kwon44 , J. W. Seo44 , I. Yu44 , A. K. Ichikawa45, K. D. Nakamura45 , S. Tairafune45 , K. Nishijima46 , K. Nakagiri47, Y. Nakajima3,47 , S. Shima47, N. Taniuchi47, E. Watanabe47, M. Yokoyama3,47 , P. de Perio3 , K. Martens3, K. M. Tsui3, M. R. Vagins3,4 , J. Xia3, M. Kuze48 , S. Izumiyama48 , R. Matsumoto48 , M. Ishitsuka49, H. Ito49 , T. Kinoshita49, R. Matsumoto49, Y. Ommura49, N. Shigeta49, M. Shinoki49 , T. Suganuma49, K. Yamauchi49, J. F. Martin50, H. A. Tanaka50, T. Towstego50, R. Gaur10, V. Gousy-Leblanc10,57, M. Hartz10, A. Konaka10, X. Li10, N. W. Prouse10,51 , S. Chen51, B. D. Xu51 , B. Zhang51, M. Posiadala-Zezula52 , S. B. Boyd53, R. Edwards53, D. Hadley53, M. Nicholson53, M. O’Flaherty53, B. Richards53, A. Ali10,54, B. Jamieson54, Ll. Marti55 , A. Minamino55 , G. Pintaudi55, S. Sano55, S. Suzuki55, K. Wada55, and The Super-Kamiokande Collaboration

1 Department of Physics, Okayama University 2 Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo 3 Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, University of Tokyo 4 Department of Physics and Astronomy, University of California 5 Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo 6 ILANCE, CNRS - University of Tokyo International Research Laboratory 7 Institute for Cosmic Ray Research, University of Tokyo 8 Department of Theoretical Physics, University Autonoma Madrid 9 Department of Physics, British Columbia Institute of Technology 10 TRIUMF 11 Department of Physics, Boston University 12 High Energy Accelerator Research Organization (KEK) 13 Department of Physics, California State University 14 Institute for Universe and Elementary Particles, Chonnam National University 15 Department of Physics, Duke University 16 Ecole Polytechnique, IN2P3-CNRS, Laboratoire Leprince-Ringuet 17 Junior College, Fukuoka Institute of Technology 18 Department of Physics, Gifu University 19 GIST College, Gwangju Institute of Science and Technology 20 Department of Physics and Astronomy, University of Hawaii 21 Institute for Basic Science (IBS) 22 Institute For Interdisciplinary Research in Science and Education, ICISE 23 Department of Physics, Imperial College London 24 Dipartimento Interuniversitario di Fisica, INFN Sezione di Bari and Università e Politecnico di Bari 25 Dipartimento di Fisica, INFN Sezione di Napoli and Università di Napoli 26 Dipartimento di Fisica, INFN Sezione di Padova and Università di Padova 27 INFN Sezione di Roma and Università di Roma "La Sapienza," 28 Department of Physics, Keio University 29 Department of Physics, King's College London 30 Department of Physics, Kobe University, Kobe 31 Department of Physics, Kyoto University, Kyoto 32 Department of Physics, University of Liverpool 33 Department of Physics, Miyagi University of Education 34 Institute for Space-Earth Environmental Research, Nagoya University 35 Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University 36 National Centre For Nuclear Research 37 Department of Physics and Astronomy, State University of New York at Stony Brook 38 Department of Physics, Oxford University 39 STFC, Rutherford Appleton Laboratory, Harwell Oxford, and Daresbury Laboratory 40 Department of Physics, Seoul National University 41 Rutherford Appleton Laboratory 42 Department of Physics and Astronomy, University of Sheffield 43 Department of Informatics in Social Welfare, Shizuoka University of Welfare 44 Department of Physics, Sungkyunkwan University 45 Department of Physics, Faculty of Science, Tohoku University 46 Department of Physics, Tokai University 47 Department of Physics, University of Tokyo 48 Department of Physics, Tokyo Institute of Technology 49 Department of Physics, Faculty of Science and Technology, Tokyo University of Science 50 Department of Physics, University of Toronto 51 Department of Engineering Physics, Tsinghua University 52 Faculty of Physics, University of Warsaw 53 Department of Physics, University of Warwick 54 Department of Physics, University of Winnipeg 55 Department of Physics, Yokohama National University