Update of the solar neutrino oscillation analysis with the 766 Ty KamLAND spectrum

Abstract

We investigate the impact of the 766.3 Ty KamLAND spectrum data on the determination of the solar neutrino oscillation parameters. We show that the observed spectrum distortion in the KamLAND experiment firmly establishes Δm²₂₁ to lie in the low-LMA solution region. The high-LMA solution is excluded at more than 4σ by the global solar neutrino and KamLAND spectrum data. The maximal solar neutrino mixing is ruled out at 6σ level. The 3σ allowed region in the Δm²₂₁ − sin²θ₁₂ plane is found to be remarkably stable with respect to leaving out the data from one of the solar neutrino experiments from the global analysis. We perform a three flavor neutrino oscillation analysis of the global solar neutrino and KamLAND spectrum data as well. The 3σ upper limit on sin²θ₁₃ is found to be sin²θ₁₃<0.055. We derive predictions for the CC to NC event rate ratio and day-night (D-N) asymmetry in the CC event rate, measured in the SNO experiment, and for the suppression of the event rate in the BOREXINO and LowNu experiments. Prospective high precision measurements of the solar neutrino oscillation parameters are also discussed.