Comprehensive analysis of beta decays within and beyond the Standard Model

Abstract

Precision measurements in allowed nuclear beta decays and neutron decay are reviewed and analyzed both within the Standard Model and looking for new physics. The analysis incorporates the most recent experimental and theoretical developments. The results are interpreted in terms of Wilson coefficients describing the effective interactions between leptons and nucleons (or quarks) that are responsible for beta decay. New global fits are performed incorporating a comprehensive list of precision measurements in neutron decay, superallowed 0+→ 0+ transitions, and other nuclear decays that include, for the first time, data from mirror beta transitions. The results confirm the V-A character of the interaction and translate into updated values for Vud and gA at the 10−4 level. We also place new stringent limits on exotic couplings involving left-handed and right-handed neutrinos, which benefit significantly from the inclusion of mirror decays in the analysis.

Top, Higgs, diboson and electroweak fit to the Standard Model effective field theory

“…riety of studies of the SMEFT, for example, in electroweak processes [106][107][108][109][110][111], flavour physics [112][113][114][115][116][117][118][119][120], low-energy precision data [121][122][123], diboson measurements [124][125][126][127][128][129][130][131], at dimension 8 [87,88,[132][133][134][135][136] (where collider positivity constraints are particularly relevant [136][137][138][139][140]), and its connection with UV-complete models, both at tree-level [141][142][143][144][145][146][147] and one-loop [148][149][150]…”

Dispersion relation analysis of the radiative corrections to gA in the neutron β-decay

“…Such a rapid development makes λ a powerful tool for searching for redBSM physics. By comparing first-principles calculations of gA to the experimental results for λ one thereby constraints the strength of possible BSM contributions that could modify g A , in particular the right-handed currents [44][45][46][47].…”

Radiative Corrections to Semileptonic Beta Decays: Progress and Challenges

“…[212] reported a percent-level determination ofg A = −1.271(10) (7) and aimed for sub-percent precision in the near future [214]. Once the lattice precision reaches 10 −3 or above, it would be possible to search for signals of BSM physics, in particular the right-handed currents [41,44,215,216], by comparing the experimental measurement of λ and the SM prediction in the right hand side of Equation (133). Due to this reason, one needs to understand the difference between A γW and V γW .…”

“…This makes the top-row CKM unitarity one of the most promising avenues for the discovery of BSM physics , in addition to the muon g − 2 [52][53][54][55][56] and the Bdecay anomalies [57][58][59][60]. Meanwhile, the various correlation coefficients in the beta decay spectrum shape also provide powerful constraints to the Wilson coefficients of possible BSM couplings in the effective field theory (EFT) representation [41][42][43][44][45][46].…”