LMA MSW solution of the solar neutrino problem and first KamLAND results

Abstract

The first KamLAND results are shown to be in very good agreement with thepredictions made on the basis of the solar neutrino data and the LMArealization of the MSW mechanism. We perform a combined analysis ofthe KamLAND (rate, spectrum) and the solar neutrino data with a freeboron neutrino flux fB. The best fit values of neutrino parametersare Δm2 = 7.3×10−5 eV2, tan2θ = 0.41 andfB = 1.05 with the 1σ intervals: Δm2 = (6.2 – 8.4)×10−5 eV2, tan2θ = 0.33 – 0.54. We find the3σ upper bounds: Δm2 < 2.8×10−4 eV2 andtan2θ < 0.84, and the lower bound Δm2 > 4×10−5 eV2. At 99% CL the KamLAND spectral result splits theLMA region into two parts with the preferred one at Δm2 < 10−4 eV2. The higher Δm2 region is accepted at about the2σ level. We show that effects of non-zero 13-mixing, sin2θ13 ⩽ 0.04, are small, leading to a slight improvement of thefit in the higher Δm2 region. At the best fit point we predictfor SNO: CC/NC = 0.33+0.05−0.03 and ADNSNO = 2.8±0.8% (68% CL), and ADNSNO < 9% at the 3σlevel. Further improvements in the determination of the oscillation parameters are discussed and implications of the solar neutrino and KamLAND results are considered.