Q value of the superallowed decay of 46V and its influence on Vud and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix -: art. no. 102501

The masses of the radioactive nuclei V-46 and its decay daughter Ti-46 have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1x10(-8). A Q(EC) value of 7052.90(40) keV for the superallowed beta decay of V-46 is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for V-46 uncovers a set of 7 measurements that cannot be reconciled with modern data and affects previous evaluations of V-ud from superallowed Fermi decays. A new evaluation, adding our new data and removing the discredited subset, yields new values for G(V) and V-ud. When combined with recent results for V-us, this yields modified constraints for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and other extensions of the standard model.