32 research outputs found
Heavy quark scattering and quenching in a QCD medium at finite temperature and chemical potential
The heavy quark collisional scattering on partons of the quark gluon plasma
(QGP) is studied in a QCD medium at finite temperature and chemical potential.
We evaluate the effects of finite parton masses and widths, finite temperature
and quark chemical potential on the different elastic cross
sections for dynamical quasi-particles (on- and off-shell particles in the QGP
medium as described by the dynamical quasi-particles model "DQPM") using the
leading order Born diagrams. Our results show clearly the decrease of the
and total elastic cross sections when the temperature and the quark
chemical potential increase. These effects are amplified for finite at
temperatures lower than the corresponding critical temperature .
Using these cross sections we, furthermore, estimate the energy loss and
longitudinal and transverse momentum transfers of a heavy quark propagating in
a finite temperature and chemical potential medium. Accordingly, we have shown
that the transport properties of heavy quarks are sensitive to the temperature
and chemical potential variations. Our results provide some basic ingredients
for the study of charm physics in heavy-ion collisions at Beam Energy Scan
(BES) at RHIC and CBM experiment at FAIR.Comment: 19 pages, 28 figure
Towards the dynamical study of heavy-flavor quarks in the Quark-Gluon-Plasma
Within the aim of a dynamical study of on- and off-shell heavy quarks Q in
the quark gluon plasma (QGP) - as produced in relativistic nucleus-nucleus
collisions - we study the heavy quark collisional scattering on partons of the
QGP. The elastic cross sections are evaluated for perturbative
partons (massless on-shell particles) and for dynamical quasi-particles
(massive off-shell particles as described by the dynamical quasi-particles
model "DQPM") using the leading order Born diagrams. We demonstrate that the
finite width of the quasi-particles in the DQPM has little influence on the
cross sections except close to thresholds. We, furthermore,
calculate the heavy quark relaxation time as a function of temperature T within
the different approaches using these cross sections.Comment: 4 pages, 5 figures, International Conference on Strangeness in Quark
Matter 2013 (SQM 2013
Collisional processes of on-shell and off-shell heavy quarks in vacuum and in the Quark-Gluon-Plasma
We study the heavy quark scattering on partons of the quark gluon plasma
(QGP) being especially interested in the collisional (elastic) scattering
processes of heavy quarks on quarks and gluons. We calculate the different
cross sections for perturbative partons (massless on-shell particles in the
vacuum) and for dynamical quasi-particles (off-shell particles in the QGP
medium as described by the dynamical quasi-particles model "DQPM") using the
leading order Born diagrams. Our results show clearly the effect of a finite
parton mass and width on the perturbative elastic cross sections which depend on temperature , energy density ,
the invariant energy and the scattering angle . Our detailed
comparisons demonstrate that the finite width of the quasi-particles in the
DQPM - which encodes the multiple partonic scattering - has little influence on
the cross section for as well as
scattering except close to thresholds. Thus when studying the dynamics of
energetic heavy quarks in a QGP medium the spectral width of the
degrees-of-freedom may be discarded. We have, furthermore, compared the cross
sections from the DQPM with corresponding results from hard-thermal-loop (HTL)
approaches. The HTL inspired models - essentially fixing the regulators by
elementary vacuum cross sections and decay amplitudes instead of properties of
the QGP at finite temperature - provide quite different results especially
w.r.t. the temperature dependence of the and cross sections (in all
settings). Accordingly, the transport properties of heavy quarks will be very
different as a function of temperature when compared to DQPM results.Comment: 28 pages, 32 figure
Transport coefficients of heavy quarks around at finite quark chemical potential
The interactions of heavy quarks with the partonic environment at finite
temperature and finite quark chemical potential are investigated in
terms of transport coefficients within the Dynamical Quasi-Particle model
(DQPM) designed to reproduce the lattice-QCD results (including the partonic
equation of state) in thermodynamic equilibrium. These results are confronted
with those of nuclear many-body calculations close to the critical temperature
. The hadronic and partonic spatial diffusion coefficients join smoothly
and show a pronounced minimum around , at as well as at finite
. Close and above its absolute value matches the lQCD calculations
for . The smooth transition of the heavy quark transport coefficients
from the hadronic to the partonic medium corresponds to a cross over in line
with lattice calculations, and differs substantially from perturbative QCD
(pQCD) calculations which show a large discontinuity at . This indicates
that in the vicinity of dynamically dressed massive partons and not
massless pQCD partons are the effective degrees-of-freedom in the quark-gluon
plasma.Comment: 4 pages, 4 figure
Heavy flavor in relativistic heavy-ion collisions
We study charm production in ultra-relativistic heavy-ion collisions by using
the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm
quarks are produced by the PYTHIA event generator tuned to fit the transverse
momentum spectrum and rapidity distribution of charm quarks from Fixed-Order
Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks
scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses
and widths are given by the Dynamical Quasi-Particle Model (DQPM), which
reproduces the lattice QCD equation-of-state in thermal equilibrium. The
relevant cross sections are calculated in a consistent way by employing the
effective propagators and couplings from the DQPM. Close to the critical energy
density of the phase transition, the charm quarks are hadronized into
mesons through coalescence and/or fragmentation. The hadronized mesons then
interact with the various hadrons in the hadronic phase with cross sections
calculated in an effective lagrangian approach with heavy-quark spin symmetry.
The nuclear modification factor and the elliptic flow of
mesons from PHSD are compared with the experimental data from the STAR
Collaboration for Au+Au collisions at =200 GeV and to the ALICE
data for Pb+Pb collisions at =2.76 TeV. We find that in the
PHSD the energy loss of mesons at high can be dominantly attributed
to partonic scattering while the actual shape of versus reflects
the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation.
Also the hadronic rescattering is important for the at low and
enhances the -meson elliptic flow .Comment: 8 pages, 3 figures, to be published in the Proceedings of the 15th
International Conference on Strangeness in Quark Matter (SQM2015), 6-11 July
2015, JINR, Dubna, Russi
Heavy-flavor production and medium properties in high-energy nuclear collisions --What next?
Open and hidden heavy-flavor physics in high-energy nuclear collisions are entering a new and exciting stage towards reaching a clearer understanding of the new experimental results with the possibility to link them directly to the advancement in lattice Quantum Chromo-Dynamics (QCD). Recent results from experiments and theoretical developments regarding open and hidden heavy-flavor dynamics have been debated at the Lorentz Workshop Tomography of the Quark-Gluon Plasma with Heavy Quarks, which was held in October 2016 in Leiden, The Netherlands. In this contribution, we summarize identified common understandings and developed strategies for the upcoming five years, which aim at achieving a profound knowledge of the dynamical properties of the quark-gluon plasma