QValue of the Superallowed Decay ofV46and Its Influence onVud

Abstract

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 x 10(-8). A Q(EC) 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 Ft 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.

Improved calculation of the isospin-symmetry-breaking corrections to superallowed Fermi β decay

“…The recent Penning-trap Q EC -value measurements [6,7] that played such an important role here should be extended to other cases so that ultimately all superallowed transitions will have been measured this way. Furthermore, the superallowed decays of T z = −1 nuclei, such as 34 Ar and 38 Ca, have large correction terms and can provide real validation of the accuracy of the calculations if they can be measured with uncertainties comparable to the currently well-known cases; such nuclei will require precise half-lives and branching ratios as well as Q EC values.…”

“…In all, more than 125 independent measurements of comparable precision, spanning four decades, made the cut. In the two years since the survey was closed, another ten relevant publications have appeared [6,7,[9][10][11][12][13][14][15][16], and we have now incorporated these results into our data base. Based on these data for the 13 most precisely known transitions, we obtain the ft values shown on the left side of Fig.…”

Precise half-life measurement of the superallowedβ+emitter46V

“…The decay of 46 V was the first of the nine best-known superallowed transitions to have its Q EC value measured (in 2005) with an on-line Penning trap [2]. The result differed significantly from the previously accepted result -a longstanding reaction-based Q EC value published in 1977 [3] -and shifted the 46 V f t value two standard deviations out of agreement with other well-known superal- * hpark@comp.tamu.edu † hardy@comp.tamu.edu lowed transitions.…”

Testing the Unitarity of the CKM Matrix With a Space-Based Neutron Decay Experiment

“…Historically, the matrix element |V ud | was determined from the super-allowed beta decays of nuclei, with difficult stronginteraction corrections applied [11]. Over time these experiments have yielded improving results, [10,12,13,14], currently yielding…”