Charmed hadron signals of partonic medium

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−D 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,c 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 v 2 of D-mesons and the low R AA (p T ) 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-p T 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.

Charm production in Pb + Pb collisions at energies available at the CERN Large Hadron Collider

“…In this study we extend our previous work and apply the PHSD to charm production in Pb+Pb collisions at √ s NN =2.76 TeV. In this way we can examine the validity and consistency of the PHSD approach in describing charm production in relativistic heavy-ion collisions in a wide range of collision energies in connection with our previous study [22] and in connection with the dynamics of light-flavor hadrons [21]. We also study the effects of parton (anti-)shadowing and of off-shell charm and anticharm quarks on the charm production and dynamics in relativistic heavy-ion collisions at the LHC.…”

“…The produced charm and anticharm quarks interact in the QGP with quarks and gluons whose masses are given by spectral functions with pole positions and widths being fitted to the lattice QCD equation-of-state (EoS) [21]. Since the contribution from charm quarks to the energy density and pressure of the QGP is small, the spectral function of a charm quark cannot be constrained by the lattice EoS.…”

Photons from the early stages of relativistic heavy-ion collisions

“…With respect to previous calculations based on transport theory [11][12][13], the main novelty that we bring by our study is the clear identification of the contribution of the early stage of RHICs to the direct photon spectrum, looking for both the relative abundance of the photons produced and the momentum region of the photon spectrum that takes the main contribution from the early stage. We will find that the early stage is quite efficient in producing photons, therefore our results support the absence of a dark age in RHICs.…”

Photon production from a nonequilibrium quark-gluon plasma

“…We also mention that there there have been recent studies that have used various types of partonic and hadronic kinetic transport codes to address the problem of photon production in heavy-ion collisions [26][27][28][29]. Such codes automatically take into account the non-equilibrium quark and gluon phase space distributions, but they ignore the effect of non-equilibrium (anisotropic) screening in the problem.…”