Tracing Remnants of the Baryon Vector Current Anomaly in Neutron Radiative Beta Decay

TL;DR

This paper explores how low-energy interactions from the baryon vector current anomaly can be isolated in neutron radiative beta decay through a specific momentum correlation, which could reveal new sources of CP violation beyond the Standard Model.

Contribution

It proposes a method to detect anomaly-induced interactions via a parity- and time-reversal-odd correlation in neutron decay, sensitive to beyond Standard Model CP violation.

Findings

Identifies a triple-product momentum correlation as a signature of anomaly-related interactions.

Analyzes the potential to set limits on new CP-violating couplings at current and future facilities.

Considers the impact of final-state interactions and extends discussion to nuclear and muon-induced decays.

Abstract

Harvey, Hill, and Hill have found that unexpected interactions involving the nucleon, photon, and weak gauge bosons at low energies emerge from gauging the axial anomaly of QCD under the full electroweak symmetry of the Standard Model (SM). In this contribution we consider how such interactions can be isolated through a triple-product momentum correlation in neutron radiative beta-decay. The correlation is both parity- and naively time-reversal-odd, so that it vanishes in the Standard Model save for effects induced by final-state interactions (FSI). Nevertheless, the correlation can be generated by sources of CP violation beyond the Standard Model, and such couplings, being spin-independent, are not constrained by the nonobservation of the neutron electric dipole moment (EDM). We consider the sorts of limits on its strength which can be determined at existing and anticipated facilities, as well as the size of induced correlations from known FSI. We also briefly consider the possibility of nuclear beta-decay studies as well as the prospects for muon-induced reaction studies.