Nuclear beta decays: time tested probes for beyond standard model physics
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Amphi G.Besse
Subatech IMT Atlantique
Massive international efforts are currently ongoing to find evidence of physics beyond the Standard Model (BSM). While some of these are focused at the high-energy, high-intensity frontier, others search for rare events using experiments conducted in deep underground laboratories or via precision tests of fundamental symmetries that are assumed in the Standard Model. In these efforts, nuclear beta decays have proven to be extremely beneficial. Two such beta decay modes - the extremely slow neutrinoless double beta (0νββ) decay and the extremely fast superallowed beta decay have played crucial roles in probing the limits of the standard model.
An observation of 0νββ decay would provide direct evidence of lepton number violation thereby signifying physics beyond the standard model. Moreover, the decay rate can be used to determine the absolute scale of neutrino masses. However, a major challenge in extracting the effective
neutrino mass from the decay half life, arises from the uncertainties associated with the calculated nuclear matrix element (NME) of the decay. In this talk, I will present how experimental nuclear structure observables have been used for constraining the NME for the 0νββ decay of 136Xe→136Ba.
0νββ decay being a lepton number violating process, requires right-handed interactions in the weak sector of the standard model. High precision measurements in allowed beta decays have been used to probe the existence of right-handed interactions. Corrected transition rates (Ƒt values) of superallowed beta decays, for instance, are sensitive to signatures of BSM physics through tests of unitarity of the CKM matrix – a cornerstone of the standard model. The currently observed ~2σ deviation from unitarity has raised questions on the theoretical corrections applied to experimental ft values. In this talk, I will present the ongoing experimental program at GANIL aimed at constraining the isospin symmetry breaking corrections for these decays.