Search for dark photons in heavy-ion collisions

TL;DR

This paper develops a method using heavy-ion collision data to set theoretical constraints on dark photon properties, aiding future experimental searches for these dark matter mediators.

Contribution

It introduces a procedure to derive upper limits on dark photon kinetic mixing parameters from various collision data using the PHSD transport model.

Findings

Established upper limits on dark photon kinetic mixing parameter $\\epsilon^2(M_U)$.

Demonstrated the PHSD model's effectiveness in reproducing dilepton spectra.

Provided guidance for future dark photon detection experiments.

Abstract

The vector $U$-bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. We present a procedure to derive theoretical constraints on the upper limit of kinetic mixing parameter $\epsilon^2(M_U)$ from heavy-ion as well as $p+p$ and $p+A$ dilepton data from SIS to LHC energies. Our study is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions well. In addition to the different dilepton channels originating from interactions and decays of ordinary Standard Model matter particles (mesons and baryons), we incorporate in the PHSD the decay of hypothetical $U$-bosons to dileptons, $U \to e^+ e^-$, where the $U$-bosons themselves are produced by the Dalitz decay of pions, $\eta$-mesons, Delta resonances as well as by vector meson and $K^+$ decays. This analysis provides the upper limit on the $\epsilon^2(M_U)$ and can also help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.