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Published June 6, 2008 | Published
Journal Article Open

Precision measurement of neutrino oscillation parameters with KamLAND


The KamLAND experiment has determined a precise value for the neutrino oscillation parameter Δm2 21 and stringent constraints on θ12. The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to 2:44 x 10 32 proton yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor ∇e energy spectrum is now rejected at >5σ. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at Δm2 21= 7.58+0.14-0.13(stat)+0.15-0.15(syst)x10-5 eV2 and tan 2θ 2=0.56+0.10-0.07(stat)+0.10-0.06(syst). Local Δχ2 minima at higher and lower Δm2 21 are disfavored at >4σ. Combining with solar neutrino data, we obtain Δm2 21 7.59+0.21-0.21 X 10-5 eV2 and tan2θ12=0.47+0.06-0.05.

Additional Information

© 2008 The American Physical Society.(Received 29 January 2008; published 5 June 2008). The KamLAND experiment is supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology, and under the United States Department of Energy Office Grant No. DEFG03-00ER41138 and other DOE grants to individual institutions. 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. PACS: 14.60.Pq; 26.65.+t; 28.50.Hw; 91.35.-x

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