APS » Phys. Rev. D » Volume 79 » Issue 11

M. Fechner,¹⁰ K. Abe,¹ Y. Hayato,^1,3 T. Iida,¹ M. Ikeda,¹ J. Kameda,¹ K. Kobayashi,¹ Y. Koshio,¹ M. Miura,¹ S. Moriyama,^1,3 M. Nakahata,^1,3 S. Nakayama,¹ Y. Obayashi,¹ H. Ogawa,¹ H. Sekiya,¹ M. Shiozawa,^1,3 Y. Suzuki,^1,3 A. Takeda,¹ Y. Takenaga,¹ Y. Takeuchi,^1,3 K. Ueno,¹ K. Ueshima,¹ H. Watanabe,¹ S. Yamada,¹ S. Hazama,² I. Higuchi,² C. Ishihara,² T. Kajita,^2,3 K. Kaneyuki,^2,3 G. Mitsuka,² H. Nishino,² K. Okumura,² N. Tanimoto,² M. R. Vagins,^3,7 F. Dufour,⁴ E. Kearns,^4,3 M. Litos,⁴ J. L. Raaf,⁴ J. L. Stone,^4,3 L. R. Sulak,⁴ W. Wang,⁴ M. Goldhaber,⁵ S. Dazeley,⁶ R. Svoboda,⁶ K. Bayes,⁷ D. Casper,⁷ J. P. Cravens,⁷ W. R. Kropp,⁷ S. Mine,⁷ C. Regis,⁷ M. B. Smy,^7,3 H. W. Sobel,^7,3 K. S. Ganezer,⁸ J. Hill,⁸ W. E. Keig,⁸ J. S. Jang,⁹ J. Y. Kim,⁹ I. T. Lim,⁹ K. Scholberg,^10,3 C. W. Walter,^10,3 R. Wendell,¹⁰ S. Tasaka,¹¹ J. G. Learned,¹² S. Matsuno,¹² Y. Watanabe,¹³ T. Hasegawa,¹⁴ T. Ishida,¹⁴ T. Ishii,¹⁴ T. Kobayashi,¹⁴ T. Nakadaira,¹⁴ K. Nakamura,^14,3 K. Nishikawa,¹⁴ Y. Oyama,¹⁴ K. Sakashita,¹⁴ T. Sekiguchi,¹⁴ T. Tsukamoto,¹⁴ A. T. Suzuki,¹⁵ A. Minamino,¹⁶ T. Nakaya,^16,3 M. Yokoyama,¹⁶ Y. Fukuda,¹⁷ Y. Itow,¹⁸ T. Tanaka,¹⁸ C. K. Jung,¹⁹ G. Lopez,¹⁹ C. McGrew,¹⁹ R. Terri,¹⁹ C. Yanagisawa,¹⁹ N. Tamura,²⁰ Y. Idehara,²¹ M. Sakuda,²¹ Y. Kuno,²² M. Yoshida,²² S. B. Kim,²³ B. S. Yang,²³ T. Ishizuka,²⁴ H. Okazawa,²⁵ Y. Choi,²⁶ H. K. Seo,²⁶ Y. Furuse,²⁷ K. Nishijima,²⁷ Y. Yokosawa,²⁷ M. Koshiba,²⁸ Y. Totsuka,²⁸ S. Chen,²⁹ Y. Heng,²⁹ Z. Yang,²⁹ H. Zhang,²⁹ D. Kielczewska,³⁰ E. Thrane,³¹ and R. J. Wilkes³¹

(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 the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
⁴Department of Physics, Boston University, Boston, Massachusetts 02215, USA
⁵Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA
⁶Department of Physics, University of California, Davis, California 95616, USA
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
⁹Department of Physics, Chonnam National University, Kwangju 500-757, Korea
¹⁰Department of Physics, Duke University, Durham, North Carolina 27708, USA
¹¹Department of Physics, Gifu University, Gifu, Gifu 501-1193, Japan
¹²Department of Physics and Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
¹³Physics Division, Department of Engineering, Kanagawa University, Kanagawa, Yokohama 221-8686, Japan
¹⁴High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
¹⁵Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan
¹⁶Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan
¹⁷Department of Physics, Miyagi University of Education, Sendai, Miyagi 980-0845, Japan
¹⁸Solar Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan
¹⁹Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3800, USA
²⁰Department of Physics, Niigata University, Niigata, Niigata 950-2181, Japan
²¹Department of Physics, Okayama University, Okayama, Okayama 700-8530, Japan
²²Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
²³Department of Physics, Seoul National University, Seoul 151-742, Korea
²⁴Department of Systems Engineering, Shizuoka University, Hamamatsu, Shizuoka 432-8561, Japan
²⁵Department of Informatics in Social Welfare, Shizuoka University of Welfare, Yaizu, Shizuoka, 425-8611, Japan
²⁶Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea
²⁷Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
²⁸The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
²⁹Department of Engineering Physics, Tsinghua University, Beijing, 100084, China
³⁰Institute of Experimental Physics, Warsaw University, 00-681 Warsaw, Poland
³¹Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA

We report the development of a proton identification method for the Super-Kamiokande (SK) detector. This new tool is applied to the search for events with a single proton track, a high purity neutral current sample of interest for sterile neutrino searches. After selection using a neural network, we observe 38 events in the combined SK-I and SK-II data corresponding to 22 85.1 days of exposure, with an estimated signal-to-background ratio of 1.6 to 1. Proton identification was also applied to a direct search for charged-current quasielastic (CCQE) events, obtaining a high precision sample of fully kinematically reconstructed atmospheric neutrinos, which has not been previously reported in water Cherenkov detectors. The CCQE fraction of this sample is 55%, and its neutrino (as opposed to antineutrino) fraction is 91.7±3%. We selected 78µ-like and 47 e-like events in the SK-I and SK-II data set. With this data, a clear zenith angle distortion of the neutrino direction itself is reported in a sub-GeV sample of µ neutrinos where the lepton angular correlation to the incoming neutrino is weak. Our fit to nu_µ-->nu_tau oscillations using the neutrino (L/E) distribution of the CCQE sample alone yields a wide acceptance region compatible with our previous results and excludes the no-oscillation hypothesis at 3-sigma.

©2009 The American Physical Society

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