Exploring Dark Photon Production and Kinetic Mixing Constraints in Heavy-Ion Collisions

TL;DR

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

Contribution

It extends the PHSD transport model to include dark photon decay channels and derives theoretical upper bounds on kinetic mixing parameters from dilepton spectra.

Findings

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

Demonstrated the model's ability to reproduce dilepton spectra across collision types

Provided guidance for future dark photon detection experiments

Abstract

Vector $U$-bosons, often referred to as 'dark photons', are potential candidates for mediating dark matter interactions. In this study, we outline a procedure to derive theoretical constraints on the upper bound of the kinetic mixing parameter $\epsilon^2(M_U)$ using dilepton data from heavy-ion from SIS to RHIC energies. The analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport model, which successfully reproduces the measured dilepton spectra in $p+p$, $p+A$, and $A+A$ collisions. Besides the dilepton channels resulting from interactions and decays of Standard Model particles (such as mesons and baryons), we extend the PHSD approach to include the decay of hypothetical $U$-bosons into dileptons, $U \to e^+ e^-$. The production of these $U$-bosons occurs via Dalitz decays of pions, $\eta$-mesons, $\omega$-mesons, Delta resonances, as well as from the decays of vector mesons and $K^+$ mesons. This analysis provides an upper limit on $\epsilon^2(M_U)$ and offers insights into the accuracy required for future experimental searches for dark photons through dilepton experiments.