Vector Meson Spectral Functions in a Coarse-Graining Approach

TL;DR

This paper models dilepton production in heavy-ion collisions using a coarse-graining approach with medium-modified spectral functions, achieving good agreement with experimental data and highlighting the impact of pion chemical potential.

Contribution

It introduces a combined microscopic and spectral function approach to calculate thermal dilepton emission, comparing two spectral models and analyzing the effects of pion chemical potential.

Findings

Both spectral functions agree well with NA60 data.

The hadronic many-body spectral function provides a better fit, especially for broadening effects.

Pion chemical potential significantly affects dilepton yields.

Abstract

Dilepton production in heavy-ion collisions at top SPS energy is investigated within a coarse-graining approach that combines an underlying microscopic evolution of the nuclear reaction with the application of medium-modified spectral functions. Extracting local energy and baryon density for a grid of small space-time cells and going to each cell's rest frame enables to determine local temperature and chemical potential by application of an equation of state. This allows for the calculation of thermal dilepton emission. We apply and compare two different spectral functions for the $\rho$: A hadronic many-body calculation and an approach that uses empirical scattering amplitudes. Quantitatively good agreement of the model calculations with the data from the NA60 collaboration is achieved for both spectral functions, but in detail the hadronic many-body approach leads to a better description, especially of the broadening around the pole mass of the $\rho$ and for the low-mass excess. We further show that the presence of a pion chemical potential significantly influences the dilepton yield.