Precision evaluation of the ${}^{71}\mathrm{Ga}({\nu }_e,e^{-})$ solar neutrino capture rate from the $\left({}^3\mathrm{He},t\right)$ charge-exchange reaction

A precision measurement of the ${}^{71}\mathrm{Ga}({}^3\mathrm{He},t){}^{71}\mathrm{Ge}$ charge-exchange reaction was performed. By using a rather complete set of theoretical form factors to describe the cross-section angular distributions over a large angular range, the Gamow-Teller strength distribution up to the effective neutron-separation energy in ${}^{71}\mathrm{Ge}$ was extracted. The data and the analysis constrain the ${}^{71}\mathrm{Ga}({\nu }_e,e^{-})$ solar neutrino rate in a neutrino nonoscillation scenario. For nonoscillating neutrinos we report a solar neutrino capture rate of $122.4\pm 3.4\left(\mathrm{stat}\right)\pm 1.1\left(\mathrm{sys}\right)$ SNU, which is lower than the presently accepted value of $132\pm 18$ SNU, though not in disagreement given the quoted errors.

Figure 1

Excitation-energy spectrum of the ${}^{71}\mathrm{Ga}({}^3\mathrm{He},t){}^{71}\mathrm{Ge}$ reaction at 420 MeV. The inset shows the isobaric analog state resonance at 8.913 MeV. Note the change of the energy scale above 5 MeV. Identified states are given with the assigned spins.

Figure 2

Angular distributions for the ${}^{71}{\mathrm{Ga}(}^3\mathrm{He},t)$ reaction leading to low-lying individual states of known spin and parity in ${}^{71}\mathrm{Ge}$. The various curves (color coded) denote the contributions from the different projectile-target angular-momentum-transfer combinations $\left[J_{\mathrm{proj}}{J}_{\mathrm{tar}}{J}_{\mathrm{rel}}\right]$. The $\left[110\right]$ contribution near zero degree is used to extract the strength of the GT transition.

Figure 3

Angular distributions for the ${}^{71}{\mathrm{Ga}(}^3\mathrm{He},t)$ reaction integrated over excitation-energy bins of 500 keV (except for 7.0 and 7.42 MeV). The various curves (color coded) denote the contributions from the different projectile-target angular-momentum-transfer combinations $\left[J_{\mathrm{proj}}{J}_{\mathrm{tar}}{J}_{\mathrm{rel}}\right]$. The $\left[110\right]$ contribution near zero degree is used to extract the GT-transition strength. Note that with increased excitation energy the GT fraction increases owing to the influence of the GTR resonance, which peaks at 11.75 MeV.

Figure 4

Cumulative SNU rates as a function of excitation energy in ${}^{71}\mathrm{Ge}$.