Weak-interaction strength from charge-exchange reactions versusβdecay in theA=40isoquintet

Abstract

We report a measurement of the Gamow-Teller (GT) strength distribution for $^{40}\mathrm{Ar}\ensuremath{\rightarrow}^{40}\mathrm{K}$ using the ${0}^{\ifmmode^\circ\else\textdegree\fi{}}(p,n)$ reaction. The measurement extends observed GT strength distribution in the $A=40$ system up to an excitation energy of $~8$ MeV. In comparing our results with those from the $\ensuremath{\beta}$ decay of the isospin mirror nucleus $^{40}\mathrm{Ti}$, we find that, within the excitation energy region probed by the $\ensuremath{\beta}$-decay experiment, we observe a total GT strength that is in fair agreement with the $\ensuremath{\beta}$-decay measurement. However, we find that the relative strength of the two strongest transitions differs by a factor of $~1.8$ in comparing our results from ($p,n$) reactions with the $\ensuremath{\beta}$ decay of $^{40}\mathrm{Ti}$. Using our results we present the neutrino-capture cross section for $^{40}\mathrm{Ar}$.