NUCLEAR-STRUCTURE DEPENDENCE OF O (ALPHA) CORRECTIONS TO FERMI DECAYS AND THE VALUE OF THE KOBAYASHI-MASKAWA MATRIX ELEMENT VUD

We calculate nuclear-structure corrections to the ft values of the eight accurately measured superallowed+ decays. The statistical fit for the average ft value is very good. The resulting new value for the matrix element of the Kobayashi-Maskawa (KM) matrix is |Vud|=0.9735(5). The error in |Vud| has thus been reduced by 50%. Combining this value for |Vud| 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. © 1990 The American Physical Society.