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The KamLAND experiment has determined a precise value for the neutrino oscillation parameter m₂₁^2 and stringent constraints on ₁₂. The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to 2. 4410^32 proton yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor {}₄ energy spectrum is now rejected at >5. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at m₂₁^2=7. 58-₀. ₁₃^+0. 14 (stat) -₀. ₁₅^+0. 15 (syst) 10^-5 eV^2 and tan^2₁₂=0. 56-₀. ₀₇^+0. 10 (stat) -₀. ₀₆^+0. 10 (syst). Local ^2 minima at higher and lower m₂₁^2 are disfavored at >4. Combining with solar neutrino data, we obtain m₂₁^2=7. 59-₀. ₂₁^+0. 2110^-5 eV^2 and tan^2₁₂=0. 47-₀. ₀₅^+0. 06.
Abe et al. (Thu,) studied this question.