Precise branching ratio measurement for the superallowed β+ decay of Si26: Completion of a second mirror pair

Superallowed $\ensuremath{\beta}$ decay is an important tool in characterizing the vector component of the weak interaction. Precise $\ensuremath{\beta}$-decay results presently give the best measurement of the up-down quark weak-mixing element, ${V}_{u\phantom{\rule{0}{0ex}}d}$. This new result completes the measurement of a second set of superallowed mirror transitions (${}^{26}$Si-${}^{26m}$Al and ${}^{26m}$Al-${}^{26}$Mg in this case) and has the precision to constrain the theoretical isospin-symmetry-breaking corrections needed in the extraction of ${V}_{u\phantom{\rule{0}{0ex}}d}$.