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

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

Figure 1

Time-of-flight (TOF) spectra obtained for ${}^{46}\mathrm{Ti}^{2+}$ (a) and ${}^{46}\mathrm{V}^{2+}$ (b) using a quadrupole excitation of 500 ms duration. The mass resolution is $\sim 5\times {10}^{-7}$.

Figure 2

Measured mass values (plotted as deviations from the tabulated mass values [10]) for the isotopes of interest versus time during the experiment.

Figure 3

Difference between the $Q$ values measured in 13 and the values obtained from all other data. The lines indicate the uncertainty on the relevant $Q$ values from the other existing data.

Figure 4

$\mathcal{F}t$ values for the most precisely known superallowed beta emitters with the modified data set.