Ftvalue of the0+→0+β+decay ofAr32: A measurement of isospin symmetry breaking in a superallowed decay

Abstract

We determined the absolute branch of the $T=2$ superallowed decay of $^{32}\mathrm{Ar}$ by detecting the ${\ensuremath{\beta}}^{+}$-delayed protons and \ensuremath{\gamma} decays of the daughter state. We obtain ${b}_{\mathrm{SA}}^{\ensuremath{\beta}}=(22.71\ifmmode\pm\else\textpm\fi{}0.16)%$, which represents the first determination of a proton branch to better than 1%. Using this branch along with the previously determined $^{32}\mathrm{Ar}$ half-life and energy release, we determined $\mathit{ft}=(1552\ifmmode\pm\else\textpm\fi{}12)$ s for the superallowed decay. This $\mathit{ft}$ value, together with the corrected $\mathcal{F}t$ value extracted from previously known $T=1$ superallowed decays, yields a measurement of the isospin symmetry breaking correction in $^{32}\mathrm{Ar}$ decay ${\ensuremath{\delta}}_{C}^{\mathrm{exp}}=(2.1\ifmmode\pm\else\textpm\fi{}0.8)%$. This can be compared to a theoretical calculation ${\ensuremath{\delta}}_{C}=(2.0\ifmmode\pm\else\textpm\fi{}0.4)%$. As by-products of this work, we determined the \ensuremath{\gamma} and proton branches for the decay of the lowest $T=2$ state of $^{32}\mathrm{Cl}$, made a precise determination of the total proton branch and relative intensities of proton groups that leave $^{31}\mathrm{S}$ in its first excited state and deduced an improved value for the $^{32}\mathrm{Cl}$ mass.