X17 – or the Search for New Physics in Nuclear Transitions

Abstract

Nuclear transitions provide a means to probe light, weakly-coupled new physics and portals into the dark sector at the MeV-scale. In this talk the so- called X-17 Anomaly will be discussed, which is a 7σ discrepancy reported by the ATOMKI group in the observation of the decays of excited 8Be and 4He nuclei to their ground states via internal e+e- pair creation. The anomaly can be explained by the emission of a neutral boson with a mass of about 17 MeV/c2. The ATOMKI results and their interpretations are discussed, as well as follow-up experiments, among which an ongoing project at the Montreal Van de Graaff accelerator facility.