Kinematic reconstruction of atmospheric neutrino events in a large water Cherenkov detector with proton identification
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 2285.1 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 νμ→ντ oscillations using the neutrino LE 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.
Fechner, M; Abe, K; Hayato, Y; Iida, T; Ikeda, M; Kameda, J; Kobayashi, K; Koshio, Y; Miura, M; Moriyama, S; Nakahata, M; Nakayama, S; Obayashi, Y; Ogawa, H; Sekiya, H; Shiozawa, M; Suzuki, Y; Takeda, A; Takenaga, Y; Takeuchi, Y; Ueno, K; Ueshima, K; Watanabe, H; Yamada, S; Hazama, S; Higuchi, I; Ishihara, C; Kajita, T; Kaneyuki, K; Mitsuka, G; Nishino, H; Okumura, K; Tanimoto, N; Vagins, MR; Dufour, F; Kearns, E; Litos, M; Raaf, JL; Stone, JL; Sulak, LR; Wang, W; Goldhaber, M; Dazeley, S; Svoboda, R; Bayes, K; Casper, D; Cravens, JP; Kropp, WR; Mine, S; Regis, C; Smy, MB; Sobel, HW; Ganezer, KS; Hill, J; Keig, WE; Jang, JS; Kim, JY; Lim, IT; Scholberg, K; Walter, CW; Wendell, R; Tasaka, S; Learned, JG; Matsuno, S; Watanabe, Y; Hasegawa, T; Ishida, T; Ishii, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Nishikawa, K; Oyama, Y; Sakashita, K; Sekiguchi, T; Tsukamoto, T; Suzuki, AT; Minamino, A; Nakaya, T; Yokoyama, M; Fukuda, Y; Itow, Y; Tanaka, T; Jung, CK; Lopez, G; McGrew, C; Terri, R; Yanagisawa, C; Tamura, N; Idehara, Y; Sakuda, M; Kuno, Y; Yoshida, M; Kim, SB; Yang, BS; Ishizuka, T; Okazawa, H; Choi, Y; Seo, HK; Furuse, Y
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