Superallowed0+→0+nuclearβdecays: A new survey with precision tests of the conserved vector current hypothesis and

Abstract

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First, we have added 27 recently published measurements and eliminated 9 references, either because they have been superseded by much more precise modern results or because there are now reasons to consider them fatally flawed; of particular importance, the new data include a number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, V ud = 0.97425 ± 0.00022. The unitarity test on the top row of the matrix becomes |V ud | 2 + |V us | 2 + |V ub | 2 = 0.99995 ± 0.00061. Both V ud and the unitarity sum have significantly reduced uncertainties compared with our previous survey, although the new value of V ud 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.

Isospin-breaking corrections to superallowed Fermiβdecay in isospin- and angular-momentum-projected nuclear density functional theory

“…Our χ 2 /n d is also higher than the perturbative-model values reported in Ref. [4] (χ 2 /n d = 1.5), shell model with Woods-Saxon (SM-WS) radial wave functions (0.4) [2], shell model with Hartree-Fock (SM-HF) radial wave functions (2.0) [3,45], Skyrme-Hartree-Fock with RPA (2.1) [11] , and relativistic Hartree-Fock plus RPA model (RHF-RPA) [12], which yields χ 2 /n d = 1.7.…”

Prospects for precision measurements in nuclear decay in the LHC era

“…In the high-energy effective theory, this bound corresponds to an effective NP scale of 11 TeV that represents a more stringent bound than those from LEP and LHC analysis on the same effective interactions [10,50]. Figure 6 90% CL limits on the scalar and tensor NP couplings Re( S,T ) from super-allowed nuclear decays [24] (green), radiative pion decay [57] (yellow) and measurements of the ratio P F /P GT [29,31] (red), along with the expected bound from future measurements of the Fierz term b in neutron decay (purple).…”

“…It is thus technically more accurate to say that a future determination of S,T from a measurement of b n at the level of 10 −3 will be dominated by the experimental error as long as Once again the use of this approximation is justified to study the effect of NP at the current level of precision, whereas sub-leading corrections have to be taken into account in the calculation of the SM contribution. This includes higher order terms in the momentum transfer expansion like weak-magnetism [22], electromagnetic effects or nuclear structure dependences [13,23,24]. Forbidden effects in allowed transitions, associated with an orbital angular momentum of the lepton pair = 0, are in principle negligible at the current level of precision due to the (qR) suppression, where R is the nucleus radius.…”

“…The most stringent limits on scalar couplings obtained from nuclear and neutron β decays arise from the contribution of the Fierz interference term to the F t-values of super-allowed pure Fermi transitions [24]. The value of the Fierz term extracted from this set reads…”

“…(16) are then due to the experimental data and to Figure 2 Constraints on real scalar couplings obtained from most precise observables in nuclear β decay. The straight lines are deduced from the Fierz interference term in super-allowed pure Fermi transitions [24]. The circular bounds are deduced from measurements of the βν angular correlation in 38m K decay [27] (red lines) and in 32 Ar [28] decay (purple lines).…”