Dielectron measurements in Au+Au collisions at BES-II energies with the STAR experiment

Department of Physics and Astronomy, Rice University, 6100 Main St, Houston, TX, 77005, USA

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Published online: 5 November 2025

Abstract

Dielectrons, emitted during the evolution of the hot and dense QCD medium created in relativistic heavy-ion collisions, offer an effective probe of the hot medium properties, as they do not involve strong interactions. The dielectron emission rate is proportional to the medium’s electromagnetic spectral function. In the dielectron mass range from 400 to 800 MeV/c², the spectral function probes the in-medium ρ meson propagator which is sensitive to the medium’s properties including the total baryon density and the temperature. By measuring thermal dielectron production, we can study the microscopic interactions between the electromagnetic current and the medium. The RHIC Beam Energy Scan (BES) program provides a unique opportunity to systematically study dielectron production in a collision energy range where the total baryon density and temperatures are varying substantially. In these proceedings, STAR measurements of thermal electrons produced in Au+Au collisions at √s_NN = 7.7, 9.2, 11.5, 14.6 and 19.6 GeV will be reported. The results will include the thermal dielectron spectra, differential/total excess yield, and the temperature extracted from the low invariant mass range, as well as their collision energy dependence.