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Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion |
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| Authors: | Araki T Eguchi K Enomoto S Furuno K Ichimura K Ikeda H Inoue K Ishihara K Iwamoto T Kawashima T Kishimoto Y Koga M Koseki Y Maeda T Mitsui T Motoki M Nakajima K Ogawa H Owada K Ricol J-S Shimizu I Shirai J Suekane F Suzuki A Tada K Tajima O Tamae K Tsuda Y Watanabe H Busenitz J Classen T Djurcic Z Keefer G McKinny K Mei D-M Piepke A Yakushev E Berger B E Chan Y D Decowski M P Dwyer D A Freedman S J Fu Y Fujikawa B K Goldman J Gray F Heeger K M Lesko K T Luk K-B Murayama H Poon A W P Steiner H M Winslow L A Horton-Smith G A Mauger C McKeown R D Vogel P Lane C E Miletic T Gorham P W Guillian G |
| Affiliation: | Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan. |
| 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 nu (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 nu (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 nu (e) oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2). A global analysis of data from KamLAND and solar-neutrino experiments yields Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2) and tan((2)theta=0.40(+0.10)(-0.07), the most precise determination to date. |
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