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Published March 4, 2005 | Published
Journal Article Open

Measurement of neutrino oscillation with KamLAND: Evidence of spectral distortion


We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 v_e candidate events with energies above 3.4 MeV compared to 365.2±23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8±7.3 expected background events, the statistical significance for reactor v_e over bar (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from v_e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2. A global analysis of data from KamLAND and solar-neutrino experiments yields Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2 and tan^2θ=0.40_(-0.07)^(+0.10), the most precise determination to date.

Additional Information

© 2005 The American Physical Society. Received 15 June 2004; published 1 March 2005. The KamLAND experiment is supported by the COE program under grant no. 09CE2003 of the Japanese Ministry of Education, Culture, Sports, Science, and Technology, and under the United States Department of Energy grant no. DEFG03-00ER41138. The reactor data are provided by courtesy of the following electric associations in Japan: Hokkaido, Tohoku, Tokyo, Hokuriku, Chubu, Kansai, Chugoku, Shikoku, and Kyushu Electric Power Companies, Japan Atomic Power Co., and Japan Nuclear Cycle Development Institute. The Kamioka Mining and Smelting Company has provided service for activities in the mine.

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August 19, 2023
August 19, 2023