title: Superallowed beta decay of nuclei with a >or= 62: the limiting effect of weak Gamow-Teller branches.
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.
authors.affiliation: Cyclotron Institute, Texas A & M University, College Station, Texas 77843, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Hardy
authors.forename: I S
authors.initials: IS
authors.lastname: Towner