Exploring non-equilibrium quark-gluon plasma effects on charm transport coefficients

Abstract

Heavy flavor particles are promising probes for the properties of the quark-gluon plasma (QGP) which is produced in relativistic heavy-ion collisions. The interaction of heavy quarks with equilibrated matter can be described by transport coefficients. In heavy-ion collisions matter is not completely thermalized. In this article we investigate how the drag coefficient A andq , the transverse momentum transfer by unit length, of charm quarks are modified if the QGP is not in complete thermal equilibrium using the dynamical quasi-particle model (DQPM) which reproduces both, the equation-of-state of the QGP and the spatial diffusion coefficient of heavy quarks as predicted by lattice quantum chromodynamics (lQCD) calculations . We study three cases: a) the QGP has an anisotropic momentum distribution of the partons which leads to an anisotropic pressure b) the QGP partons have higher or lower kinetic energies as compared to the thermal expectation value, and c) the QGP partons have larger or smaller pole masses of their spectral function as compared to the pole mass from the DQPM at the QGP temperature. In the last two cases we adjust the number density of partons to obtain the same energy density as in an equilibrated QGP.In the first scenario we find that if the transverse pressure exceeds the longitudinal one for small heavy quark momenta A becomes larger andq smaller as compared to an isotropic pressure. For heavy quarks with large momentum both, A andq , approach unity. If the partons have less kinetic energy or a smaller pole mass as compared to a system in equilibrium charm quarks lose more energy. In the former caseq decreases whereas in the latter case it increases for charm quark with a low or intermediate transverse momentum. Thus each non-equilibrium scenario affects A andq of charm quarks in a different way. The modifications in our scenarios are of the order 20-50 % at temperatures relevant for heavy ion reactions. These modifications have to be considered if one wants to determine these coefficients by comparing heavy ion data with theoretical predictions from viscous hydrodynamics or Langevin equations.

Heavy quark diffusion in an overoccupied gluon plasma

“…The authors find that the glasma phase can have a sizable contribution to momentum broadening and energy loss of heavy quarks. At later stages of the non-equilibrium evolution when the quasiparticle description is valid, recent studies have indicated that the pre-equilibrium effects can be important [14,15]. In [16] jet momentum broadening in the glasma was investigated.…”

Holographic vector mesons in a dilaton background

“…Such a behavior could be interpreted as preformation of modes which turn upon cooling into the corresponding quasi-particles at lower temperatures. We leave the investigation of spectral functions to separate follow-up work and focus on implications of (3) - (9).…”

“…Since heavy quarks emerge essentially in early, hard processes, they witness the course of a heavy-ion collision -either as individual entities or subjects of dissociating and regenerating bound states [2,3,4]. Accordingly, the heavy-quark physics addresses such issues as charm (c,c) and bottom (b,b) dynamics related to transport coefficients [5,6,7,8,9] in the rapidly evolving and highly anisotropic ambient quark-gluon medium [10,11] as well as cc / bb states as open quantum systems [12,13,14,15]. The rich body of experimental data from LHC, and also from RHIC, enabled a tremendous refinement of our theoretical treatment which grew up on initiating ideas like "Mott mechanism and the hadronic to quark matter matter phase transition" [16], "J/ψ suppression by quark-gluon plasma formation" [17], "Dissociation kinetics and momentum dependent J/ψ suppression" [18], and "Statistical hadronization of charm in heavy ion collisions at SPS, RHIC and LHC" [19].…”

Quarkonia Formation in a Holographic Gravity–Dilaton Background Describing QCD Thermodynamics

“…Since heavy quarks essentially emerge in early, hard processes, they witness the course of heavy-ion collision-either as individual entities or subjects of dissociating and regenerating bound states [3][4][5]. Accordingly, the heavy-quark physics addresses such issues as charm (c,c) and bottom (b,b) dynamics related to transport coefficients [6][7][8][9][10] in the rapidly evolving and highly anisotropic ambient quark-gluon medium [11,12] as well as cc and bb states as open quantum systems [13][14][15][16]. The rich body of experimental data from LHC, and also from RHIC , enabled a tremendous refinement of our understanding of heavy-quark dynamics.…”