New limits on fundamental weak-interaction parameters from superallowed beta decay.
A new survey of all world data on superallowed beta decays provides demanding tests of, and tight constraints on, the weak interaction. In confirmation of the conserved vector current hypothesis, the vector coupling constant G(V) is demonstrated to be constant to better than three parts in 10(4), and any induced scalar current is limited to f(S)</=0.0013 in electron rest-mass units. Any possible fundamental scalar current is similarly limited to /C(S)/C(V)/</=0.0013. The superallowed data also determine the up-down element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix to be V(ud)=0.9738(4). With Particle Data Group values for V(us) and V(ub), the top-row test of CKM unitarity yields /V(ud)/(2)+/V(us)/(2)+/V(ub)/(2)=0.9966(14); if V(us) comes instead from two recent results on K(e3) decay, this sum becomes 0.9996(11). Either unitarity result can be used to constrain the possible existence of right-hand currents.
Hardy
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JC
Cyclotron Institute, Texas A&M University, College Station, Texas 77843, USA.
Towner
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