Superallowed0+→0+nuclearβdecays: 2014 critical survey, with precise results forVudand CKM unitarity

Precise measurements of the $\ensuremath{\beta}$ decay between nuclear states of spin-parity ${0}^{+}$ and isospin 1 provide fundamental tests of the properties of the electroweak interaction. Collectively, these transitions sensitively probe the conservation of the vector weak current, set tight limits on the presence of scalar currents, and provide the most precise value for ${V}_{u\phantom{\rule{0}{0ex}}d}$. The latter result has become a linchpin in the most demanding test of the unitarity of the CKM matrix.