Update on Chiral Symmetry Restoration in the Context of Dilepton Data

TL;DR

This paper reviews dilepton and photon emission data from heavy-ion collisions to understand in-medium effects and their relation to chiral symmetry restoration, linking experimental signatures with theoretical models and lattice QCD results.

Contribution

It provides a comprehensive analysis of electromagnetic spectral functions and their flow signatures, connecting experimental data with chiral symmetry restoration in hot and dense matter.

Findings

Melting of the $ ho$ resonance correlates with chiral symmetry restoration.

In-medium modifications of spectral functions are consistent with lattice QCD results.

Flow signatures help pinpoint the emission history of electromagnetic radiation.

Abstract

We evaluate currently available information on low-mass dilepton and direct-photon emission spectra measured in ultrarelativistic heavy-ion collisions. In the first part an attempt is made to develop a consistent picture of the in-medium effects on the electromagnetic spectral function and pinpoint its emission history by utilizing its radial and elliptic flow signatures. In the second part we elaborate on the implications of the empirical information on the nature of chiral symmetry restoration. We indicate how the melting of the $\rho$ resonance in hot and dense matter is related to, and compatible with, the reduction of chiral order parameters as "measured" in thermal lattice QCD.