Superallowed 0(+)-> 0(+) nuclear beta decays: A critical survey with tests of the conserved vector current hypothesis and the standard model

Abstract

A complete and critical survey is presented of all half-life, decay-energy, and branching-ratio measurements related to 20 superallowed 0(+)-> 0(+) decays

no measurements are ignored, although some are rejected for cause and others updated. A new calculation of the statistical rate function f is described and experimental ft values determined. The associated theoretical corrections needed to convert these results into "corrected" Ft values are discussed, and careful attention is paid to the origin and magnitude of their uncertainties. As an exacting confirmation of the conserved vector current hypothesis, the corrected Ft values are seen to be constant to three parts in 10(4). These data are also used to set a new limit on any possible scalar interaction (assuming maximum parity violation) of C-S/C-V = -(0.00005 +/- 0.00130). The average Ft value obtained from the survey, when combined with the muon liftime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, V-ud = 0.9738 +/- 0.0004, and the unitarity test on the top row of the matrix becomes vertical bar V(ud)vertical bar(2) + vertical bar V(us)vertical bar(2) + vertical bar V(ub)vertical bar(2) = 0.9966 +/- 0.0014 using the Particle Data Group's currently recommended values for V-us and V-ub. If V-us comes instead from two recent results on K-e3 decay, the unitarity sum becomes 0.9996(11). Either result can be expressed in terms of the possible existence of right-hand currents. Finally, we discuss the priorities for future theoretical and experimental work with the goal of making the CKM unitarity test more definitive.