Charmed hadron signals of partonic medium

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 byD−D̄ 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, c̄ 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 RAA(pT ) of J/Ψ 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/Ψ rapidity distribution from pp to central Au+Au collisions at the top RHIC energy. We demonstrate additionally that the strong quenching of high-pT J/Ψ’s in central Au + Au collisions indicates that a fraction of final J/Ψ mesons is created by a coalescence mechanism close to the phase boundary.