In-medium Spectral Functions in a Coarse-Graining Approach

TL;DR

This paper employs a coarse-graining method to derive local thermodynamic properties from microscopic transport simulations, then calculates thermal dilepton yields using different spectral functions for the rho meson, comparing results to experimental data.

Contribution

It introduces a coarse-graining approach to connect microscopic transport models with thermal dilepton production, comparing two spectral functions for the rho meson against experimental data.

Findings

Both spectral functions describe the data reasonably well.

The hadronic many-body spectral function better matches the in-medium broadening.

The approach provides a good framework for analyzing dilepton yields in heavy-ion collisions.

Abstract

We use a coarse-graining approach to extract local thermodynamic properties from simulations with a microscopic transport model by averaging over a large ensemble of events. Setting up a grid of small space-time cells and going into each cell's rest frame allows to determine baryon and energy density. With help of an equation of state we get the corresponding temperature $T$ and baryon-chemical potential $\mu_{\mathrm{B}}$. These results are used for the calculation of the thermal dilepton yield. We apply and compare two different spectral functions for the $\rho$ meson, firstly a calculation from hadronic many-body theory and secondly a calculation from experimental scattering amplitudes. The results obtained with our approach are compared to measurements of the NA60 Collaboration. A relatively good description of the data is achieved with both spectral functions. However, the hadronic many-body calculation is found to be closer to the experimental data with regard to the in-medium broadening of the spectral shape.