Superallowed 0+→0+ nuclear β decays: A new survey with precision tests of the conserved vector current hypothesis and the standard model
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A new critical survey is presented of all half-life, decay-energy, and branching-ratio measurements related to 20 superallowed 0+→0+β decays. Compared with our last review, there are numerous improvements: First, we have added 27 recently published measurements and eliminated 9 references, either because they have been superseded by much more precise modern results or because there are now reasons to consider them fatally flawed; of particular importance, the new data include a number of high-precision Penning-trap measurements of decay energies. Second, we have used the recently improved isospin symmetry-breaking corrections, which were motivated by these new Penning-trap results. Third, our calculation of the statistical rate function f now accounts for possible excitation in the daughter atom, a small effect but one that merits inclusion at the present level of experimental precision. Finally, we have re-examined the systematic uncertainty associated with the isospin symmetry-breaking corrections by evaluating the radial-overlap correction using Hartree-Fock radial wave functions and comparing the results with our earlier calculations, which used Saxon-Woods wave functions; the provision for systematic uncertainty has been changed as a consequence. The new "corrected" Ft values are impressively constant and their average, when combined with the muon lifetime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, Vud=0.97425±0.00022. The unitarity test on the top row of the matrix becomes |Vud|2+|Vus|2+|Vub|2=0. 99995±0.00061. Both Vud and the unitarity sum have significantly reduced uncertainties compared with our previous survey, although the new value of Vud is statistically consistent with the old one. From these data we also set limits on the possible existence of scalar interactions, right-hand currents, and extra Z bosons. Finally, we discuss the priorities for future theoretical and experimental work with the goal of making the CKM unitarity test even more definitive. © 2009 The American Physical Society.
author list (cited authors)
Hardy, J. C., & Towner, I. S.