The evaluation ofV_udand its impact on the unitarity of the Cabibbo–Kobayashi–Maskawa quark-mixing matrix

Abstract

We have written an invited review article [1] on the determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element V ud. Data from 0 + → 0 + superallowed beta decay in nuclei, neutron decay, beta decay of odd-mass mirror nuclei and pion decay were considered. Theoretical radiative and isospin symmetry-breaking corrections were applied. The most precise result comes from the nuclear 0 + → 0 + decays, which yield a recommended value of |V ud | = 0.97425(22). We further summarized the data leading to the CKM matrix element V us : K l3 and K l2 decays, hyperon decays and hadronic tau decay. Again radiative corrections and SU(3)-symmetry breaking corrections (from lattice QCD) were applied. We adopted values from K l3 decay of |V us | = 0.2246(12) and from K l2 decay of |V us /V ud | = 0.2319(14). From the three data just cited, a least-squares fit determines two CKM matrix elements: |V ud | = 0.97425(22) and |V us | = 0.22521(94). Data leading to the third member of the top row of the CKM matrix, V ub , were summarized as well but, being of order 10-3 , that matrix element contributes negligibly to the unitarity sum, |V ud | 2 + |V us | 2 + |V ub | 2. We found this sum to be 0.99990(60), showing unitarity to be satisfied to a precision of 0.06%. We also discussed the constraints that this result places on several selected extensions to the standard model.

Prospects for precision measurements in nuclear decay in the LHC era

“…The opportunities for improving the errors of the F t-values have recently been discussed in Ref. [3] in connection with the determination of V ud from pure Fermi transitions for the unitarity test of the CKM matrix. The other measured observable providing complementary constraints to those resulting from the F tvalues is the βν angular correlation a.…”

“…The tests of the SM and the searches for New Physics (NP) in nuclear and neutron decays have been the subject of several recent reviews, with focus either on experiments in nuclear β decay [2][3][4][5] or on experiments using cold or ultra-cold neutrons [6][7][8].…”

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

“…The latter pertain to calculations of radiative processes and -for nuclear methods -to the nuclear ISB effect. The uncertainties in radiative and ISB corrections affect the overall precision of V ud at the level of a few parts per 10 4 each [1,51]. It should be stressed, however, that the ISB contribution to the error bar of V ud was calculated only for a single theoretical model (SM-WS).…”

Beta-Decay Studies in N ≈ Z Nuclei Using No-Core Configuration-Interaction Model

“…In particular, these data are needed for testing unitarity of the CKM matrix, violation of which may signalize new physics beyond the Standard Model, see [1] and refs. quoted therein.…”