Production and evolution path of dileptons at HADES energies

TL;DR

This paper analyzes dilepton production in intermediate energy nucleus-nucleus and proton-proton collisions using the UrQMD model, comparing results with HADES data and exploring the effects of particle absorption on dilepton yields.

Contribution

It provides new predictions for dilepton spectra at various energies and investigates the impact of particle absorption, enhancing understanding of dilepton production mechanisms at HADES energies.

Findings

The model slightly overestimates the spectrum at 2 AGeV near the vector meson peak.

At 1 AGeV, the model underestimates the data, indicating incomplete saturation by standard Dalitz decays.

Predictions for dilepton spectra in proton-proton and Ar+KCl reactions are presented.

Abstract

Dilepton production in intermediate energy nucleus-nucleus collisions as well as in elementary proton-proton reactions is analysed within the UrQMD transport model. For C+C collisions at 1 AGeV and 2 AGeV the resulting invariant mass spectra are compared to recent HADES data. We find that the experimental spectrum for C+C at 2 AGeV is slightly overestimated by the theoretical calculations in the region around the vector meson peak, but fairly described in the low mass region, where the data is satisfactorily saturated by the Dalitz decay of the $\eta$ meson and the $\Delta$ resonance. At 1 AGeV an underestimation of the experimental data is found, pointing that at lower energies the low mass region is not fully saturated by standardly parametrized $\Delta$ Dalitz decays alone. Furthermore, predictions for dilepton spectra for $pp$ reactions at 1.25 GeV, 2.2 GeV and 3.5 GeV and Ar+KCl reactions at 1.75 AGeV are presented. The study is complemented by a detailed investigation of the role of absorption of the parent particles on the corresponding dilepton yields in the regime which has so far been probed by HADES.