Search for electron neutrino appearance in a 250 km long-baseline experiment

• Published in: Physical review letters Vol. 93; no. 5; pp. 051801.1 - 051801.5
• Main Authors: AHN, M. H, AOKI, S, HARA, T, HASEGAWA, M, HASEGAWA, T, HAYASHI, K, HAYATO, Y, HILL, J, ICHIKAWA, A. K, IKEDA, A, INAGAKI, T, ISHIDA, T, ASHIE, Y, ISHII, T, ISHITSUKA, M, ITOW, Y, IWASHITA, T, JANG, H. I, JANG, J. S, JEON, E. J, JOO, K. K, JUNG, C. K, KAJITA, T, BHANG, H, KAMEDA, J, KANEYUKI, K, KATO, I, KEARNS, E, KIBAYASHI, A, KIELCZEWSKA, D, KIM, B. J, KIM, C. O, KIM, J. Y, KIM, S. B, BOYD, S, KOBAYASHI, K, KOBAYASHI, T, KOSHIO, Y, KROPP, W. R, LEARNED, J. G, LIM, S. H, LIM, I. T, MAESAKA, H, MARUYAMA, T, MATSUNO, S, CASPER, D, MAUGER, C, MCGREW, C, MINAMINO, A, MINE, S, MIURA, M, MIYANO, K, MORITA, T, MORIYAMA, S, NAKAHATA, M, NAKAMURA, K, CHOI, J. H, FUKUDA, S, FUKUDA, Y, GRAN, R
• Format: Journal Article
• Language: English
• Published: Ridge, NY American Physical Society 30-07-2004
• Subjects: Astronomical and space-research instrumentation; Astronomy; Earth, ocean, space; Exact sciences and technology; Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations; Leptons; Neutrino interactions; Neutrino mass and mixing; Neutrino, muon, pion, and other elementary particle detectors; cosmic ray detectors; Physics; Properties of specific particles; Specific reactions and phenomenology; The physics of elementary particles and fields; Neutrino oscillations; Electron neutrinos
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/physrevlett.93.051801

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).