The Gallium Neutrino Absorption Cross Section and its Uncertainty

The recent Baksan Experiment on Sterile Transitions (BEST) reported a suppressed rate of neutrino absorption on a gallium target, consistent with earlier results from calibration studies of the SAGE and GALLEX/GNO solar neutrino experiments. This discrepancy between expected vs. observed neutrino captures is known as the gallium anomaly, which some have cited as possible evidence for new neutrino physics. To predict the expected capture rate for a given incident neutrino flux, one must know the neutrino capture cross section on ⁷¹Ga, a common systematic of all five gallium experiments. The original BEST analysis used a cross section value computed by Bahcall in 1997. Here, we update the gallium neutrino absorption cross section. To establish both a central value and reasonable uncertainty, we consider a variety of electroweak corrections as well as contributions from transitions to excited states. In the latter case, we carefully extract Gamow-Teller operator strengths from (p,n) and (³He, t) scattering data. These various corrections result in a central value for the neutrino absorption cross section that is reduced by 2% from the value employed in the original BEST analysis. As a result, the significance of the gallium anomaly is slightly reduced, but still stands at roughly 4 standard deviations.