Beta decays and non-standard interactions in the LHC era

Abstract

We consider the role of precision measurements of beta decays and light meson semi-leptonic decays in probing physics beyond the Standard Model in the LHC era. We describe all low-energy charged-current processes within and beyond the Standard Model using an effective field theory framework. We first discuss the theoretical hadronic input which in these precision tests plays a crucial role in setting the baseline for new physics searches. We then review the current and upcoming constraints on the various non-standard operators from the study of decay rates, spectra, and correlations in a broad array of light-quark systems. We finally discuss the interplay with LHC searches, both within models and in an effective theory approach. Our discussion illustrates the independent yet complementary nature of precision beta decay measurements as probes of new physics, showing them to be of continuing importance throughout the LHC era.

Framework for maximum likelihood analysis of neutronβdecay observables to resolve the limits of theV−Alaw

“…A bag model estimate gives g 2 /g V ∼ 0.3 [72] in |∆S| = 1 semileptonic transitions. More recently, non-zero second-class currents have been observed in quenched lattice QCD calculations of form factors which appear in the hyperon semileptonic decay Ξ 0 → Σ + ℓν, yielding f 3 /g V = 0.14(9) and g 2 /g A = 0.68 (18) [73]. Turning to the nucleon sector, we expect these estimates to be suppressed, crudely, by m d /m s ∼ 0.1.…”

“…Of the future experimental plans reviewed in Refs. [11][12][13][14][15][16][17][18][19], the claim of ultimate precision rests with the PERC experiment [20], for a sensitivity of up to 10 −4 precision.…”

Prospects for precision measurements in nuclear decay in the LHC era

“…Like for the CP-conserving coefficients, the ratio R π = (π → eν)/ (π → μν) offers strong constraints on Im( S,T ) since they generate radiatively a non-zero Im( P ) [11].…”

“…(17) is given in Eq. (11). Assuming first that the sensitivity to tensor couplings arises only via the Fierz term, we then set a ≈ a SM ≈ −1/3.…”

“…We confront next the most precise results obtained in β decay with constraints obtained from other semileptonic processes and also with results from the LHC [9][10][11], paying special attention to those observables that are linear on the exotic couplings. The use of an Effective Field Theory (EFT) framework allows us to bridge through the low energy and the high energy searches and to compare their sensitivities to new physics.…”