Speaker
Description
Vector $U$-bosons, commonly known as 'dark photons', are hypothesized mediators of dark matter interactions. In this study, we establish a methodology to set theoretical constraints on the upper limit of the kinetic mixing parameter $\varepsilon^2(M_U)$ by analyzing dilepton spectra from heavy-ion collisions spanning SIS to LHC energies. Our approach relies on the microscopic Parton-Hadron-String Dynamics (PHSD) transport model, which accurately describes measured dilepton production in $p+p$, $p+A$, and $A+A$ collisions. In addition to the conventional dilepton sources from Standard Model processes, such as mesonic and baryonic interactions and decays, we extend the PHSD framework to incorporate dilepton decays of hypothetical $U$-bosons via $U \to e^+ e^-$. These $U$-bosons are produced via Dalitz decays of $\pi$, $\eta$, $\eta^{\prime}$, and $\omega$ mesons, as well as $\Delta$ resonances. Additional contributions arise from the decays of vector mesons $\rho,\omega,\phi$ and $K^+$ mesons. Our findings impose an upper bound on $\varepsilon^2(M_U)$ and highlight the precision required for future experimental searches for dark photons in dilepton channels.