Charm production in Pb+Pb collisions at the Large Hadron Collider energy

TL;DR

This paper investigates charm quark production and dynamics in Pb+Pb collisions at LHC energies using a transport model, comparing results with experimental data and exploring effects of off-shell charm quarks and energy loss mechanisms.

Contribution

It introduces a detailed transport approach for charm quarks in heavy-ion collisions, including off-shell effects and hadronization, providing new insights into charm quark interactions and flow.

Findings

Reasonable agreement of $R_{AA}$ and elliptic flow with experimental data.

Off-shell charm quarks have moderate effects on scattering cross sections.

Radiative energy loss effects are small compared to collisional loss up to 15 GeV/c.

Abstract

We study charm production in Pb+Pb collisions at $\sqrt{s_{\rm NN}}=$2.76 TeV in the Parton-Hadron-String-Dynamics transport approach and the charm dynamics in the partonic and hadronic medium. The charm quarks are produced through initial binary nucleon-nucleon collisions by using the PYTHIA event generator taking into account the (anti-)shadowing incorporated in the EPS09 package. The produced charm quarks interact with off-shell massive partons in the quark-gluon plasma and are hadronized into $D$ mesons through coalescence or fragmentation close to the critical energy density, and then interact with hadrons in the final hadronic stage with scattering cross sections calculated in an effective Lagrangian approach with heavy-quark spin symmetry. The PHSD results show a reasonable $R_{\rm AA}$ and elliptic flow of $D$ mesons in comparison to the experimental data for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV from the ALICE Collaboration. We also study the effect of temperature-dependent off-shell charm quarks in relativistic heavy-ion collisions. We find that the scattering cross sections are only moderately affected by off-shell charm degrees of freedom. However, the position of the peak of $R_{\rm AA}$ for $D$ mesons depends on the strength of the scalar partonic forces which also have an impact on the $D$ meson elliptic flow. The comparison with experimental data on the $R_{\rm AA}$ suggests that the repulsive force is weaker for off-shell charm quarks as compared to that for light quarks. Furthermore, the effects from radiative charm energy loss appear to be low compared to the collisional energy loss up to transverse momenta of $\sim$ 15 GeV/c.