Search for Dark Photons in $\gamma \gamma \to e^{+}{e}^{-}$ 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 $\mathrm{Au}+\mathrm{Au}$ collisions. This study utilizes measurements of the Breit-Wheeler process ($\gamma \gamma \to e^{+}{e}^{-}$) 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.

6 pages, 3 figures