Abstract
The KamLAND experiment uses reactor antineutrinos to study the solar neutrino oscillation parameters. KamLAND recently updated the reactor neutrino measurement, with an almost fourfold increase of the exposure, an improved analysis technique and better understanding of the backgrounds and systematic uncertainties. Extending the analysis down to the inverse beta decay energy threshold gives a best-fit at Δm221 = 7.58+0.14-0.13(stat)+0.15-0.15(syst) × 10−5 eV2 and tan2 θ12 = 0.56+0.10-0.07(stat)+0.10-0.06(syst). Local Δχ2-minima at higher and lower Δm221 are now disfavored at >4σ. When combined with solar neutrino data, we obtain Δm221 = 7.59+0.21-0.21 × 10−5 eV2 and tan2 θ12 = 0.47+0.06-0.05. KamLAND is presently purifying the detector to measure solar 7Be neutrinos in the near future.
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