The Gallium Solar Neutrino Capture Cross Section Revisited

TL;DR

This paper reevaluates the gallium solar neutrino capture cross section using updated nuclear physics calculations, leading to refined cross section values that impact solar neutrino flux analyses.

Contribution

It introduces a correction for tensor operator contributions in excited-state transitions and combines multiple updates to improve cross section estimates.

Findings

Lowered $^8$B and hep neutrino cross sections due to tensor correction.

Overall increase (~10%) in $^8$B and hep cross sections after including additional corrections.

Uncertainties propagated via Monte Carlo simulations.

Abstract

Solar neutrino flux constraints from the legacy GALLEX/GNO and SAGE experiments continue to influence contemporary global analyses of neutrino properties. The constraints depend on the neutrino absorption cross sections for various solar sources. Following recent work updating the $^{51}$Cr and $^{37}$Ar neutrino source cross sections, we reevaluate the $^{71}$Ga solar neutrino cross sections, focusing on contributions from transitions to $^{71}$Ge excited states, but also revising the ground-state transition to take into account new $^{71}$Ge electron-capture lifetime measurements and various theory corrections. The excited-state contributions have been traditionally taken from forward-angle $(p,n)$ cross sections. Here we correct this procedure for the $\approx 10\%-20\%$ tensor operator contribution that alters the relationship between Gamow-Teller and $(p,n)$ transition strengths. Using state-of-the-art nuclear shell-model calculations to evaluate this correction, we find that it lowers the $^8$B and hep neutrino cross sections. However, the addition of other corrections, including contributions from near-threshold continuum states that radiatively decay, leads to an overall increase in the $^8$B and hep cross sections of $\approx 10\%$ relative to the values recommended by Bahcall. Uncertainties are propagated using Monte Carlo simulations.