Dilepton production and reaction dynamics in heavy-ion collisions at SIS energies from coarse-grained transport simulations

Abstract

Dilepton invariant-mass spectra for heavy-ion collisions at SIS 18 and BEVALAC energies are calculated using a coarse-grained time evolution from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. The coarse-graining of the microscopic simulations enables to calculate thermal dilepton emission rates by application of in-medium spectral functions from equilibrium quantum-field theoretical calculations. The results show that extremely high baryon chemical potentials dominate the evolution of the created hot and dense fireball. Consequently, a significant modification of the $\rho$ spectral shape becomes visible in the dilepton invariant-mass spectrum, resulting in an enhancement in the low-mass region $M_{ee}=200$ to 600 MeV/$c^2$. This enhancement, mainly caused by baryonic effects on the $\rho$ spectral shape, can fully describe the experimentally observed excess above the hadronic cocktail contributions in Ar+KCl ($E_{\mathrm{lab}}=1.76$ $A$GeV) reactions as measured by the HADES collaboration and also gives a good explanation of the older DLS Ca+Ca ($E_{\mathrm{lab}}=1.04$ $A$GeV) data. For the larger Au+Au ($E_{\mathrm{lab}}=1.23$ $A$GeV) system, we predict an even stronger excess from our calculations. A systematic comparison of the results for different system sizes from C+C to Au+Au shows that the thermal dilepton yield increases stronger ($\propto A^{4/3}$) than the hadronic background contributions, which scale with $A$, due to its sensitivity on the time evolution of the reaction. We stress that the findings of the present work are consistent with our previous coarse-graining results for the NA60 measurements at top SPS energy. We argue that it is possible to describe the dilepton results from SIS 18 up to SPS energies by considering the modifications of the $\rho$ spectral function inside a hot and dense medium within the same model.

15 pages, 9 figures

References in corpus (20)

• Fully integrated transport approach to heavy ion reactions with an intermediate hydrodynamic stage
• Highly-anisotropic and strongly-dissipative hydrodynamics for early stages of relativistic heavy-ion collisions
• Comprehensive Interpretation of Thermal Dileptons at the SPS
• Dilepton production and off-shell transport dynamics at SIS energies
• Dielectron production in Ar+KCl collisions at 1.76A GeV
• Study of dielectron production in C+C collisions at 1 AGeV
• Low Mass Dimuons Produced in Relativistic Nuclear Collisions
• Thermal Dimuon Yields at NA60
• Dilepton production in proton-induced reactions at SIS energies with the GiBUU transport model
• Low mass dilepton production at ultrarelativistic energies
• Production and evolution path of dileptons at HADES energies
• A coarse-graining approach for dilepton production at SPS energies
• Dilepton production in proton-proton and quasifree proton-neutron reactions at 1.25 GeV
• Dimuon radiation at the CERN SPS within a (3+1)d hydrodynamic+cascade model
• Dilepton yields from Brown-Rho scaled vector mesons including memory effects
• Phase Structure in a Hadronic Chiral Model
• Dilepton production at SIS energies with the GiBUU transport model
• In-medium Spectral Functions in a Coarse-Graining Approach
• Vector Meson Spectral Functions in a Coarse-Graining Approach
• Dilepton Production in Transport-based Approaches

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