Is ρ-meson melting compatible with chiral restoration?

Abstract

Utilizing in-medium vector spectral functions which describe dilepton data in ultra-relativistic heavy-ion collisions, we conduct a comprehensive evaluation of QCD and Weinberg sum rules at finite temperature. The starting point is our recent study in vacuum, where the sum rules have been quantitatively satisfied using phenomenological vector and axial-vector spectral functions which describe hadronic τ-decay data. In the medium, the temperature dependence of condensates and chiral order parameters is taken from thermal lattice QCD where available, and otherwise is estimated from a hadron resonance gas. Since little is known about the in-medium axial-vector spectral function, we model it with a Breit–Wigner ansatz allowing for smooth temperature variations of its width and mass parameters. Our study thus amounts to testing the compatibility of the ρ-broadening found in dilepton experiments with (the approach toward) chiral restoration, and thereby searching for viable in-medium axial-vector spectral functions.