Dilepton production and resonance properties within a new hadronic transport approach in the context of the GSI-HADES experimental data

TL;DR

This paper introduces a new hadronic transport model called SMASH for dilepton production in heavy-ion collisions, validating it against HADES data and exploring medium effects on vector mesons in larger systems.

Contribution

The paper presents the SMASH transport approach for dilepton emission, incorporating vacuum resonance properties and medium modifications, validated against experimental data.

Findings

Excellent agreement with HADES data for small systems.

Medium effects significantly influence dilepton spectra in larger systems.

Transport approach with vacuum properties captures key features of dilepton production.

Abstract

The dilepton emission in heavy-ion reactions at low beam energies is examined within a hadronic transport approach. In this article the production of electron-positron pairs from a new approach named SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) is introduced. The dilepton emission is consistently taken into account below the hadronic threshold. The calculations are systematically confronted with HADES data in the kinetic energy range of $1 - 3.5A$ GeV for elementary, proton-nucleus and nucleus-nucleus reactions. The present approach employing a resonance treatment based on vacuum properties is validated by an excellent agreement with experimental data up to system sizes of carbon-carbon collisions. After establishing this well-understood baseline in elementary and small systems, the significance of medium effects is investigated with a coarse-graining approach based on the same hadronic evolution. The effect of explicit in-medium modifications to the vector meson spectral functions is important for dilepton invariant mass spectra in ArKCl and larger systems, even though the transport approach with vacuum properties reveals similar features due the coupling to baryonic resonance and the intrinsically included collisional broadening. This article provides a comprehensive comparison of our calculations with published dielectron results from the HADES collaboration. In addition, the emission of dileptons is predicted in gold-gold and pion-beam experiments for which results are expected soon.