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

We determined the absolute branch of the $T=2$ superallowed decay of ${}^{32}\mathrm{Ar}$ by detecting the ${\beta }^{+}$-delayed protons and γ decays of the daughter state. We obtain $b_{\mathrm{SA}}^{\beta }=(22.71\pm 0.16)\%$, 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 $\mathit{ft}=(1552\pm 12)$ 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 ${\delta }_C^{\exp }=(2.1\pm 0.8)\%$. This can be compared to a theoretical calculation ${\delta }_C=(2.0\pm 0.4)\%$. As by-products of this work, we determined the γ 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.