Search for Dark Photons in $\gamma\gamma\rightarrow e^+e^-$ at RHIC

Abstract

The fundamental nature of Dark Matter remains one of the major mysteries of modern physics. Some models postulate the existence of a massive gauge boson, a "dark photon" ($A^\prime$), that may allow Dark Matter particles to interact with Standard Model particles. Ultra-relativistic heavy-ion collisions produce highly Lorentz-contracted electromagnetic fields with sufficient energy density to potentially manifest as light dark photons. We report limits on dark photon parameters via a search for anomalous production of $e^+e^-$ pairs in $\gamma A^\prime$ and $A^\prime A^\prime$ fusion from ultra-peripheral $\rm{Au}+\rm{Au}$ collisions. This study utilizes measurements of the Breit-Wheeler process ($\gamma\gamma \rightarrow e^+e^-$) carried out by STAR, specifically making use of polarization-dependent final-state azimuthal asymmetries in $e^+e^-$ pairs. These limits are informative for future searches in the ultra-peripheral heavy-ion collisions and to constrain future theoretical developments of the dark photon mechanism.