The theoretical side of β-decay new physics searches

The Standard Model (SM) of particle physics describes all known elementary particles and fundamental forces, excluding gravity. There is, however, growing evidence that the Standard Model is incomplete. Recent years have seen an extensive effort put into finding evidence for interactions beyond the Standard Model (BSM) of physics, making use of precision measurements of nuclear beta-decays in different nuclei. To identify these BSM signatures, experimental measurements must be compared with accurate theoretical predictions. In this talk, I will introduce this experimental surge, motivating me to develop the theoretical formalism required for the analysis of experiments currently being conducted. Presenting a new approach for decomposing tensor interactions of fermionic probes within the multipole analysis, I will examine how signatures of new physics appear in the correlations between the particles emitted in β-decays, and in the energy spectrum of allowed and forbidden decays, which I will show that have an increased sensitivity to these signatures. In addition, to be able to distinguish between new physics signatures and high orders of the known SM physics, I will describe a general framework, suitable for any nucleus and any decay, enabling precise calculations of β-decay observables required for ongoing experiments, with controlled accuracy, evaluated by identifying a hierarchy of small parameters related to the low momentum transfer that characterizes β-decays. First applications to 6He and 23Ne β-decay ongoing measurements at the SARAF accelerator, Israel, will be presented, resulting in new constraints on BSM tensor interactions, and paving the way for new, even more accurate, experiments and discoveries.