366 research outputs found
Collective flow in central Au-Au collisions at 150, 250 and 400 A MeV
Radial collective flow and thermalization are studied in gold on gold
collisions at 150, 250 and 400 A MeV bombarding energies with a
relativistically covariant formulation of a QMD code. We find that radial flow
and "thermal" energies calculated for all the charged fragments agree
reasonably with the experimental values. The experimental hardware filter at
small angles used in the FOPI experiments at higher energies selects mainly the
thermalized particles.Comment: 4 pages with 4 EPS figures included. Version accepted for publication
in Phys. Rev.
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
Modelling the many-body dynamics of heavy ion collisions: Present status and future perspective
Basic problems of the semiclassical microscopic modelling of strongly
interactingsystems are discussed within the framework of Quantum Molecular
Dynamics (QMD). This model allows to study the influence of several types of
nucleonic interactions on a large variety of observables and phenomena
occurring in heavy ion collisions at relativistic energies.It is shown that the
same predictions can be obtained with several -- numerically completely
different and independently written -- programs as far as the same model
parameters are employed and the same basic approximations are made. Many
observables are robust against variations of the details of the model
assumptions used. Some of the physical results, however, depend also on rather
technical parameters like the preparation of the initial configuration in phase
space. This crucial problem is connected with the description of the ground
state of single nuclei,which differs among the various approaches. An outlook
to an improved molecular dynamics scheme for heavy ion collisions is given.Comment: 39 pages, 12 figure
Particle-particle correlations and the space-time structure of heavy ion collisions
The present status of the use of two-particle intensity interferometry as a
diagnostic tool to study the space-time dynamics of intermediate energy heavy
ion collisions is examined. Calculations for the two-proton and two-pion
correlation functions are presented and compared to experiment. The
calculations are based on the nuclear Boltzmann-Uehling-Uhlenbeck transport
theory.Comment: 20 pages, Preprint MSUCL-864 (to be published in Progress in Particle
and Nuclear Physics, Vol. 30
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