Nuclear-structure dependence ofO(α)corrections to Fermi decays and the value of the Kobayashi-Maskawa matrix elementVud

We calculate nuclear-structure corrections to the $\mathrm{ft}$ values of the eight accurately measured superallowed ${\beta }^{+}$ decays. The statistical fit for the average $\mathrm{ft}$ value is very good. The resulting new value for the matrix element of the Kobayashi-Maskawa (KM) matrix is $\left|V_{\mathrm{ud}}\mathrm{}\right|=0.9735\left(5\mathrm{}\right)\mathrm{}$. The error in $\left|V_{\mathrm{ud}}\right|$ has thus been reduced by 50%. Combining this value for $\left|V_{\mathrm{ud}}\right|$ with the presently accepted results from kaon-, hyperon-, and $B$-decay constraints, the unitarity of the KM matrix for three generations of quarks seems to be violated.