Superallowed beta decay of nuclei with a >or= 62: the limiting effect of weak Gamow-Teller branches

Phys Rev Lett. 2002 Jun 24;88(25 Pt 1):252501. doi: 10.1103/PhysRevLett.88.252501. Epub 2002 Jun 6.

Abstract

The most precise value of V(ud), which is obtained from superallowed nuclear beta decay, leads to a violation of Cabibbo-Kobayashi-Maskawa unitarity by 2.2sigma. Experiments are underway on two continents to test and improve this result through decay studies of odd-odd N = Z nuclei with A>or=62. We show, in a series of illustrative shell-model calculations, that numerous weak Gamow-Teller branches are expected to compete with the superallowed branch in each of these nuclei. Though the total Gamow-Teller strength is significant, many of the individual branches will be unobservably weak. Thus, new techniques must be developed if reliable ft values are to be obtained with 0.1% precision for the superallowed branches.