Solar neutrinos with magnetic moment: rates and global analysis

A statistical analysis of the solar neutrino data is presented assuming the solar neutrino deficit to be resolved by the resonant interaction of the neutrino magnetic moment with the solar magnetic field. Four field profiles are investigated, all exhibiting a rapid increase across the bottom of the convective zone, one of them closely following the requirements from recent solar physics investigations. First a `rates onlyʹ analysis is performed whose best fits appear to be remarkably better than all fits from oscillations. A global analysis then follows with the corresponding best fits of a comparable quality to the LMA one. Despite the fact that the resonant spin flavour precession does not predict any day/night effect, the separate SuperKamiokande day and night data are included in the analysis in order to allow for a direct comparison with oscillation scenarios. Remarkably enough, the best fit for rates and global analysis which is compatible with most astrophysical bounds on the neutrino magnetic moment is obtained from the profile which most closely follows solar physics requirements. Allowing for a peak field value of 3×105 G, it is found in this case that Δm221=1.45×10−8 eV2, μν=3.2×10−12μB (65% CL). The new forthcoming experiments on solar neutrino physics (Kamland and Borexino) will be essential to ascertain whether this fact is incidental or essential.