Beam Energy Dependence of Dielectron Production in Au+Au Collisions from STAR at RHIC

TL;DR

This study measures dielectron production in gold-gold collisions at various energies at RHIC, comparing results to models and highlighting a consistent enhancement in the low-mass region across energies, informing future research directions.

Contribution

It provides the first systematic energy-dependent dielectron measurements in Au+Au collisions at RHIC energies, comparing data to theoretical models of in-medium rho modifications.

Findings

Consistent dielectron enhancement in the low-mass region across energies.

Model describes the enhancement within uncertainties from SPS to RHIC energies.

Data supports the understanding of in-medium rho modifications in hot nuclear matter.

Abstract

We present the energy-dependent study of dielectron production in 0-80% minimum-bias Au+Au collisions at $\sqrt{s_{NN}}$ energies of 19.6, 27, 39, and 62.4 GeV in STAR. Invariant mass ($M_{ee}$) and transverse momentum ($p_T$) differential measurements of dielectron yields are compared to cocktail simulations of known hadronic sources and semi-leptonic charmed decays. The enhancement (excess yield) prominent in the Low-Mass Region (LMR) over the cocktail at all energies, is further compared to calculations of $\rho$ in-medium modifications. Within statistical and systematic uncertainties, we find that the model consistently describes this enhancement from SPS up to top RHIC energies in its $M_{ee}$- as well as $p_T$-dependence. Dielectron measurements drive the statistics for the future BES Phase-II program, which promises to improve our understanding of the LMR enhancement's trend with total baryon densities.