Measurement of neutrino oscillation with KamLAND: Evidence of spectral distortion

T. Araki*, K. Eguchi, S. Enomoto, K. Furuno, K. Ichimura, H. Ikeda, K. Inoue, K. Ishihara, T. Iwamoto, T. Kawashima, Y. Kishimoto, M. Koga, Y. Koseki, T. Maeda, T. Mitsui, M. Motoki, K. Nakajima, H. Ogawa, K. Owada, J. S. RicolI. Shimizu, J. Shirai, F. Suekane, A. Suzuki, K. Tada, O. Tajima, K. Tamae, Y. Tsuda, H. Watanabe, J. Busenitz, T. Classen, Z. Djurcic, G. Keefer, K. McKinny, D. M. Mei, A. Piepke, E. Yakushev, B. E. Berger, Y. D. Chan, M. P. Decowski, D. A. Dwyer, S. J. Freedman, Y. Fu, B. K. Fujikawa, J. Goldman, F. Gray, K. M. Heeger, K. T. Lesko, K. B. Luk, H. Murayama, A. W.P. Poon, H. M. Steiner, L. A. Winslow, G. A. Horton-Smith, C. Mauger, R. D. McKeown, P. Vogel, C. E. Lane, T. Miletic, P. W. Gorham, G. Guillian, J. G. Learned, J. Maricic, S. Matsuno, S. Pakvasa, S. Dazeley, S. Hatakeyama, A. Rojas, R. Svoboda, B. D. Dieterle, J. Detwiler, G. Gratta, K. Ishii, N. Tolich, Y. Uchida, M. Batygov, W. Bugg, Y. Efremenko, Y. Kamyshkov, A. Kozlov, Y. Nakamura, C. R. Gould, H. J. Karwowski, D. M. Markoff, J. A. Messimore, K. Nakamura, R. M. Rohm, W. Tornow, R. Wendell, A. R. Young, M. J. Chen, Y. F. Wang, F. Piquemal

*Corresponding author for this work

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Abstract

We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 ν̄e 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 ν̄e 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 ν̄e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm2 = 7.9 +0.5+0.6 × 10-5 eV2. A global analysis of data from KamLAND and solar-neutrino experiments yields Δm2 = 7.90.50.6 × 10-5 eV2 and tan2θ = 0.400.07+0.10 the most precise determination to date.

Original languageEnglish
Article number081801
JournalPhysical Review Letters
Volume94
Issue number8
DOIs
Publication statusPublished - 4 Mar 2005
Externally publishedYes

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