Mentoring Award: Can a photophobic vector boson explain the ATOMKI anomaly?

In 2016, the ATOMKI collaboration announced the observation an unexpected enhancement of the electron-positron pair production signal in one of the nuclear transitions induced by an incident proton beam on a 7Li target. This finding led to many beyond-standard-model physics explanations. One popular theory is that the anomaly is caused by the creation of a protophobic vector boson (X) with a mass around 17 MeV the nuclear transition. We studied [2] this hypothesis by deriving an isospin relation between photon and X couplings to nucleons. This allowed us to find simple relations between protophobic X-production cross sections and those for measured photon production. The net result is that X production can be dominated by direct transitions induced by and (transverse and longitudinal electric dipoles) and (charge dipole) without going through any nuclear resonance (i.e. Bremsstrahlung radiation) with a smooth energy dependence that occurs for all proton beam energies above threshold. This work caused the ATOMKI [3] and other collaborations to search for the production of X particles in non-resonant transitions. An update will be provided.

1. A.J. Krasznahorkay, et al., Phys. Rev. Lett. 116, 042501 (2016)]

2. X. Zhang and G. A. Miller, Phys. Lett. B813, 136061 (2021)

3. N. J. Sas et al., arXiv:2205.07744 [nucl-ex]