Elliptic flow and $R_{AA}$ of D mesons at FAIR comparing the UrQMD hybrid model and the coarse-graining approach

TL;DR

This study compares two modeling approaches for D meson elliptic flow and R_AA in Au+Au collisions at FAIR energies, highlighting the importance of the partonic phase and medium dynamics in charm quark behavior.

Contribution

It introduces a comparative analysis of UrQMD hybrid and coarse-graining models for charm meson observables at FAIR energies, emphasizing the role of the partonic phase.

Findings

Initial partonic phase generates most of the D meson elliptic flow.

Hadronic interactions have minor impact on elliptic flow.

Charm quarks are effective probes of the Quark-Gluon Plasma at FAIR energies.

Abstract

We present a study of the elliptic flow and $R_{AA}$ of D and anti-D mesons in Au+Au collisions at FAIR energies. We propagate the charm quarks and the D mesons following a previously applied Langevin dynamics. The evolution of the background medium is modeled in two different ways: (I) we use the UrQMD hydrodynamics + Boltzmann transport hybrid approach including a phase transition to QGP and (II) with the coarse-graining approach employing also an equation of state with QGP. The latter approach has previously been used to describe di-lepton data at various energies very successfully. This comparison allows us to explore the effects of partial thermalization and viscous effects on the charm propagation. We explore the centrality dependencies of the collisions, the variation of the decoupling temperature and various hadronization parameters. We find that the initial partonic phase is responsible for the creation of most of the D mesons elliptic flow and that the subsequent hadronic interactions seem to play only a minor role. This indicates that D mesons elliptic flow is a smoking gun for a partonic phase at FAIR energies. However, the results suggest that the magnitude and the details of the elliptic flow strongly depend on the dynamics of the medium and on the hadronization procedure, which is related to the medium properties as well. Therefore, even at FAIR energies the charm quark might constitute a very useful tool to probe the Quark-Gluon Plasma and investigate its physics.