Gallium solar neutrino experiments: Absorption cross sections, neutrino spectra, and predicted event rates

Abstract

Neutrino absorption cross sections for ${}^{71}\mathrm{Ga}$ are calculated for all solar neutrino sources with standard energy spectra, and for laboratory sources of ${}^{51}\mathrm{Cr}$ and ${}^{37}\mathrm{Ar}$; the calculations include, where appropriate, the thermal energy of fusing solar ions and use improved nuclear and atomic data. The ratio, $R,$ of measured (in GALLEX and SAGE) to calculated ${}^{51}\mathrm{Cr}$ capture rate is $R$=0.95\ifmmode\pm\else\textpm\fi{}0.07 (expt)${+}_{\mathrm{\ensuremath{-}}0.03}^{+0.04}$ (theor). Cross sections are also calculated for specific neutrino energies chosen so that a spline fit determines accurately the event rates in a gallium detector even if new physics changes the energy spectrum of solar neutrinos. Theoretical uncertainties are estimated for cross sections at specific energies and for standard neutrino energy spectra. Standard energy spectra are also presented for $\mathrm{pp}$ and CNO neutrino sources in the appendix. Neutrino fluxes predicted by standard solar models, corrected for diffusion, have been in the range 120 SNU to 141 SNU since 1968.