Dilepton production in microscopic transport theory with in-medium $\rho$-meson spectral function

TL;DR

This paper employs a microscopic transport model to study dilepton production in heavy-ion collisions, emphasizing the in-medium broadening of the $ ho$-meson and comparing results with experimental data to improve understanding of in-medium effects.

Contribution

It introduces a calculation of the $ ho$-meson collisional width in nuclear matter within the GiBUU model and compares the effects with experimental dilepton spectra, improving the theoretical description.

Findings

Collisional broadening enhances agreement with experimental dilepton spectra.

Adjusting $pn$ bremsstrahlung cross section improves data description.

In-medium effects are significant near the $ ho$ pole mass.

Abstract

We use the microscopic GiBUU transport model to calculate dilepton ($e^+e^-$) production in heavy-ion collisions at SIS18 energies focusing on the effect of collisional broadening of the $\rho$-meson. The collisional width of the $\rho$-meson at finite temperature and baryon density in nuclear matter is calculated on the basis of the collision integral of the GiBUU model. A systematic comparison with HADES data on dilepton production in heavy-ion collisions is performed. The collisional broadening of the $\rho$ improves the agreement between theory and experiment for the dilepton invariant-mass distributions near the $\rho$ pole mass and for the excess radiation in Au+Au at $1.23 A$ GeV. We furthermore show that some remaining underprediction of the experimental dilepton spectra in C+C at $1 A$ GeV and Au+Au at $1.23 A$ GeV at intermediate invariant masses $0.2-0.4$ GeV can be accounted for by adjusting the $pn$ bremsstrahlung cross section in a way to agree with the inclusive dilepton spectrum from $dp$ collisions at $1.25 A$ GeV.