Solar neutrino rates, spectrum, and its moments: an MSW analysis in the light of Super-Kamiokande results

Abstract

We reexamine Mikheyev-Smirnov-Wolfenstein (MSW) solutions of the solar neutrino problem in a two flavor scenario taking (a) the results on total rates and the electron energy spectrum from the 1117-day SuperKamiokande (SK) data and (b) those on total rates from the chlorine and gallium experiments. We find that the small mixing angle (SMA) solution gives the best fit to the total rates data from the different experiments. One new feature of our analysis is the use of the moments of the SK electron spectrum in a χ² analysis. The best-fit to the moments is broadly in agreement with that obtained from a direct fit to the spectrum data, and prefers a Δm² comparable to the rates of the SMA fit, but the required mixing angle is larger. In the combined rate and spectrum analysis, apart from varying the normalization of the ⁸B flux as a free parameter and determining its best-fit value, we also obtain the best-fit parameters when correlations between the rates and the spectrum data are included, and the normalization of the ⁸B flux is held fixed at its standard solar model (SSM) value. We observe that the correlations between the rates and spectrum data are important, and the goodness of fit worsens when these are included. In either case, the best-fit lies in the LMA region.