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

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 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 , , and 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, . The production of these U ‐bosons occurs via Dalitz decays of pions, η ‐mesons, ω ‐mesons, Delta resonances, as well as from the decays of vector mesons and mesons. This analysis provides an upper limit on and offers insights into the accuracy required for future experimental searches for dark photons through dilepton experiments.