124 research outputs found
Towards an understanding of the RHIC single electron data
High transverse momentum () single non-photonic electrons which have
been measured in the RHIC experiments come dominantly from heavy meson decay.
The ratio of their spectra in pp and AA collisions ()
reveals the energy loss of heavy quarks in the environment created by AA
collisions. Using a fixed coupling constant and the Debye mass () as infrared regulator perturbative QCD (pQCD) calculations are not able to
reproduce the data, neither the energy loss nor the azimuthal
distribution. Employing a running coupling constant and replacing the Debye
mass by a more realistic hard thermal loop (HTL) calculation we find a
substantial increase of the collisional energy loss which brings the
distribution as well as to values close to the experimental ones
without excluding a contribution from radiative energy loss.Comment: Accepted for publication in Physical Review
Radiative energy loss of relativistic charged particles in absorptive media
We determine the energy loss spectrum per time-interval of a relativistic
charge traversing a dispersive medium. Polarization and absorption effects in
the medium are modelled via a complex index of refraction. We find that the
spectrum amplitude becomes exponentially damped due to absorption mechanisms.
Taking explicitly the effect of multiple scatterings on the charge trajectory
into account, we confirm results obtained in a previous work.Comment: 4 pages, Proceedings of the 5th International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2012),
27 May - 1 June 2012, Cagliari, Ital
Energy loss of a heavy quark produced in a finite-size quark-gluon plasma
We study the energy loss of an energetic heavy quark produced in a high
temperature quark-gluon plasma and travelling a finite distance before emerging
in the vacuum. While the retardation time of purely collisional energy loss is
found to be of the order of the Debye screening length, we find that the
contributions from transition radiation and the Ter-Mikayelian effect do not
compensate, leading to a reduction of the zeroth order (in an opacity
expansion) energy loss.Comment: QM2006 Proceedings; caption of fig 1 and ref [7] modified in v
Impact of gluon damping on heavy-quark quenching
In this conference contribution, we discuss the influence of
gluon-bremsstrahlung damping in hot, absorptive QCD matter on the heavy-quark
radiation spectra. Within our Monte-Carlo implementation for the description of
the heavy-quark in-medium propagation we demonstrate that as a consequence of
gluon damping the quenching of heavy quarks becomes significantly affected at
higher transverse momenta.Comment: Proceedings for Heavy Ion Collisions in the LHC Era, Vietnam
Conference: C12-07-1
The multifragmentation of spectator matter
We present the first microscopic calculation of the spectator fragmentation
observed in heavy ion reactions at relativistic energies which reproduces the
slope of the kinetic energy spectra of the fragments as well as their
multiplicity, both measured by the ALADIN collaboration. In the past both have
been explained in thermal models, however with vastly different assumptions
about the excitation energy and the density of the system. We show that both
observables are dominated by dynamical processes and that the system does not
pass a state of thermal equilibrium. These findings question the recent
conjecture that in these collisions a phase transition of first order, similar
to that between water and vapor, can be observed.Comment: 7 page
Competition of Heavy Quark Radiative and Collisional Energy Loss in Deconfined Matter
We extend our recently advanced model on collisional energy loss of heavy
quarks in a quark gluon plasma (QGP) by including radiative energy loss. We
discuss the approach and present first preliminary results. We show that
present data on nuclear modification factor of non photonic single electrons
hardly permit to distinguish between those 2 energy loss mechanisms.Comment: 8 pages, extended to 11 pages for v2; accepted for publication in
Journal of Physics
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
Non-universality of transverse Coulomb exchange at small x
Within an explicit scalar QED model we compare, at fixed x << 1, the
leading-twist K_T-dependent `quark' distribution f_q(x, K_T) probed in deep
inelastic scattering and Drell-Yan production, and show that the model is
consistent with the universality of f_q(x, K_T). The extension of the model
from the aligned-jet to the 'symmetric' kinematical regime reveals interesting
properties of the physics of Coulomb rescatterings when comparing DIS and DY
processes. At small x the transverse momentum induced by multiple
scattering on a single centre is process dependent, as well as the transverse
momentum broadening occurring in collisions on a finite size nuclear target.Comment: 28 pages, 3 eps figure
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