Q Value of the Superallowed Decay of $^{46}$V and Its Influence on $V_ud$ and the Unitarity of the Cabibbo-Kobayashi-Maskawa Matrix

• Published in: Physical review letters 2005, Vol.95
• Main Authors: Savard, G., Buchinger, F., Clark, J.A., Crawford, J.E., Gulick, S., Hardy, J.C., Hecht, A.A., Lee, J. K. P., Levand, A.F., Scielzo, N.D., Sharma, H., Sharma, K.S., Tanihata, I., Villari, A.C.C., Wang, Y.
• Format: Article
• Language: English
• Subjects: Nuclear Experiment; Physics
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.95.102501

The masses of the radioactive nuclei $^{46}$V and its decay daughter $^{46}$Ti have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1$\times10^{-8}$. A QEC value of 7052.90(40) keV for the superallowed beta decay of $^{46}$V is obtained from the difference of these two masses. With this precise Q value, the [script F]t value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for $^{46}$V 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.