Precision measurement of neutrino oscillation parameters with KamLAND

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The KamLAND experiment has determined a precise value for the neutrino oscillation parameter Δm212 and stringent constraints on θ12. The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to 2.44×1032protonyr due to longer livetime and an enlarged fiducial volume. An undistorted reactor ν̄e 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 Δm212=7.58-0.13+0.14(stat)-0.15+0.15(syst)×10-5eV2 and tan 2θ12=0.56-0.07+0.10(stat)-0.06+0.10(syst). Local Δχ2 minima at higher and lower Δm212 are disfavored at >4σ. Combining with solar neutrino data, we obtain Δm212=7.59-0.21+0.21×10-5eV2 and tan 2θ12=0.47-0.05+0.06. © 2008 The American Physical Society.

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