Charmed hadron signals of partonic medium

TL;DR

This paper reviews charmed hadron behavior in heavy-ion collisions, emphasizing the importance of partonic interactions over hadronic ones at RHIC energies to explain experimental observations like flow and suppression patterns.

Contribution

It demonstrates that partonic and pre-hadronic interactions are essential to accurately model charm dynamics and quark-gluon plasma effects in heavy-ion collisions.

Findings

Hadronic 'comover' absorption explains SPS data but not RHIC.

Partonic interactions dominate charm dynamics at RHIC energies.

Coalescence contributes to J/Psi production near the phase boundary.

Abstract

We present a short review of our results on the collectivity and the suppression pattern of charmed mesons in heavy-ion collisions based on the microscopic Hadron-String Dynamics (HSD) transport approach for different scenarios of charm interactions with the surrounding matter - the 'comover' dissociation by mesons with further recreation by D+Dbar channels and 'pre-hadronic' interaction scenarios. While at SPS energies the hadronic 'comover' absorption scenario is found to be compatible with the experimental data, the dynamics of c and cbar quarks at RHIC are dominated by partonic or 'pre-hadronic' interactions in the strongly coupled quark-gluon plasma stage and cannot be modeled by pure hadronic interactions. We find that the collective flow of charm in the purely hadronic scenario appears compatible with the data at SPS energies but underestimates the data at top RHIC energies. Thus, the large elliptic flow v2 of D mesons and the low R_AA(pT) of J/Psi seen experimentally at RHIC have to be attributed to early interactions of non-hadronic degrees of freedom. Simultaneously, we observe that non-hadronic interactions are mandatory in order to describe the narrowing of the J/Psi rapidity distribution from p+p to central Au+Au collisions at the top RHIC energy. We demonstrate additionally that the strong quenching of high-pT J/Psi's in central Au+Au collisions indicates that a fraction of final J/Psi mesons is created by a coalescence mechanism close to the phase boundary.