  In the recent Baksan Experiment on Sterile Transitions (BEST), a suppressed
rate of neutrino absorption on a gallium target was observed, consistent with
earlier results from neutrino source calibrations of the SAGE and GALLEX/GNO
solar neutrino experiments. The BEST collaboration, utilizing a 3.4 MCi 51Cr
neutrino source, found observed-to-expected counting rates at two very short
baselines of R=0.791 plus/minus 0.05 and 0.766 plus/minus 0.05, respectively.
Among recent neutrino experiments, BEST is notable for the simplicity of both
its neutrino spectrum, line neutrinos from an electron-capture source whose
intensity can be measured to a estimated precision of 0.23%, and its absorption
cross section, where the precisely known rate of electron capture to the
gallium ground state, 71Ge(e,nue)71Ga(g.s.), establishes a minimum value.
However, the absorption cross section uncertainty is a common systematic in the
BEST, SAGE, and GALLEX/GNO neutrino source experiments. Here we update that
cross section, considering a variety of electroweak corrections and the role of
transitions to excited states, to establish both a central value and reasonable
uncertainty, thereby enabling a more accurate assessment of the statistical
significance of the gallium anomalies. Results are given for 51Cr and 37Ar
sources. The revised neutrino capture rates are used in a re-evaluation of the
BEST and gallium anomalies.
