New Limits on Fundamental Weak-Interaction Parameters from Superallowed β Decay

A new survey of all world data on superallowed β 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 10⁴, 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.