Search for electron neutrino appearance in a 250 km long-baseline experiment.
We present a search for electron neutrino appearance from accelerator-produced muon neutrinos in the K2K long-baseline neutrino experiment. One candidate event is found in the data corresponding to an exposure of 4.8 x 10(19) protons on target. The expected background in the absence of neutrino oscillations is estimated to be 2.4+/-0.6 events and is dominated by misidentification of events from neutral current pi(0) production. We exclude the nu(micro) to nu(e) oscillations at 90% C.L. for the effective mixing angle in the 2-flavor approximation of sin((2)2theta(microe)( approximately 1/2sin((2)2theta(13))>0.15 at Deltam(2)(microe)=2.8 x 10(-3) eV(2), the best-fit value of the nu(micro) disappearance analysis in K2K. The most stringent limit of sin((2)2theta(microe)<0.09 is obtained at Deltam(2)(microe)=6 x 10(-3) eV(2).
Ahn, MH; Aoki, S; Ashie, Y; Bhang, H; Boyd, S; Casper, D; Choi, JH; Fukuda, S; Fukuda, Y; Gran, R; Hara, T; Hasegawa, M; Hasegawa, T; Hayashi, K; Hayato, Y; Hill, J; Ichikawa, AK; Ikeda, A; Inagaki, T; Ishida, T; Ishii, T; Ishitsuka, M; Itow, Y; Iwashita, T; Jang, HI; Jang, JS; Jeon, EJ; Joo, KK; Jung, CK; Kajita, T; Kameda, J; Kaneyuki, K; Kato, I; Kearns, E; Kibayashi, A; Kielczewska, D; Kim, BJ; Kim, CO; Kim, JY; Kim, SB; Kobayashi, K; Kobayashi, T; Koshio, Y; Kropp, WR; Learned, JG; Lim, SH; Lim, IT; Maesaka, H; Maruyama, T; Matsuno, S; Mauger, C; Mcgrew, C; Minamino, A; Mine, S; Miura, M; Miyano, K; Morita, T; Moriyama, S; Nakahata, M; Nakamura, K; Nakano, I; Nakata, F; Nakaya, T; Nakayama, S; Namba, T; Nambu, R; Nishikawa, K; Nishiyama, S; Noda, S; Obayashi, Y; Okada, A; Oyama, Y; Pac, MY; Park, H; Saji, C; Sakuda, M; Sarrat, A; Sasaki, T; Sasao, N; Scholberg, K; Sekiguchi, M; Sharkey, E; Shiozawa, M; Shiraishi, KK; Smy, M; Sobel, HW; Stone, JL; Suga, Y; Sulak, LR; Suzuki, A; Suzuki, Y; Takeuchi, Y; Tamura, N; Tanaka, M; Totsuka, Y; Ueda, S; Vagins, MR; Walter, CW; Wang, W; Wilkes, RJ; Yamada, S; Yamamoto, S; Yanagisawa, C; Yokoyama, H; Yoo, J; Yoshida, M; Zalipska, J; K2K Collaboration,
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