Super-Kamiokande hep neutrino best fit: a possible signal of non-Maxwellian solar plasma

The super-Kamiokande best global fit, which includes data from SNO, gallium and chlorine experiments, results in a hep neutrino contribution to the signals that, even after oscillation, is greater than the SSM prediction. The solar hep neutrino flux that would yield this contribution is four times larger than the one predicted by the SSM. Recent detailed calculations exclude that the astrophysical factor Shep(0) could be wrong by such a large factor. Given the reliability of the temperature and density profiles inside the sun, this experimental result indicates that plasma effects are important for this reaction. We show that a slight enhancement of the high-energy tail, enhancement that is of the order of the deviations from the Maxwell–Boltzmann distribution expected in the solar core plasma and that can be effectively described, for instance, by the non-extensive generalized statistical mechanics, produces an increment of the hep rate of the magnitude required. We verified that the other neutrino fluxes remain compatible with experimental signals and SSM predictions. Better measurements of the high-energy tail of the neutrino spectrum would improve our understanding of reaction rates in the solar plasma.