The solar neutrino problem after the first results from KamLAND

Abstract

The first results from the KamLAND experiment have provided confirmational evidence for the Large Mixing Angle (LMA) Mikheyev-Smirnov-Wolfenstein (MSW) solution to the solar neutrino problem. We do a global analysis of solar and the recently announced KamLAND data (both rate and spectrum) and investigate its effect on the allowed region in the Δm²-tan²θ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at Δm²=6.06×10⁻⁵ eV² and tan²θ =0.42, very close to the global solar best-fit, leaving a large allowed region within the global solar LMA contour. The inclusion of the KamLAND spectral data in the global fit gives a best-fit Δ m²=7.17×10⁻⁵ eV² and tan²θ =0.43 and constrains the allowed areas within LMA, leaving essentially two allowed zones. Maximal mixing though allowed by the KamLAND data alone is disfavored by the global solar data and remains disallowed at about 3σ . The low Δ m²solution (LOW) is now ruled out at about 5σ with respect to the LMA solution.