3,910 research outputs found
Heavy-Quark Diffusion and Hadronization in Quark-Gluon Plasma
We calculate diffusion and hadronization of heavy quarks in high-energy
heavy-ion collisions implementing the notion of a strongly coupled quark-gluon
plasma in both micro- and macroscopic components. The diffusion process is
simulated using relativistic Fokker-Planck dynamics for elastic scattering in a
hydrodynamic background. The heavy-quark transport coefficients in the medium
are obtained from non-perturbative -matrix interactions which build up
resonant correlations close to the transition temperature. The latter also form
the basis for hadronization of heavy quarks into heavy-flavor mesons via
recombination with light quarks from the medium. The pertinent resonance
recombination satisfies energy conservation and provides an equilibrium mapping
between quark and meson distributions. The recombination probability is derived
from the resonant heavy-quark scattering rate. Consequently, recombination
dominates at low transverse momentum () and yields to fragmentation at
high . Our approach thus emphasizes the role of resonance correlations in
the diffusion and hadronization processes. We calculate the nuclear
modification factor and elliptic flow of - and -mesons for Au-Au
collisions at the Relativistic Heavy Ion Collider, and compare their
decay-electron spectra to available data. We also find that a realistic
description of the medium flow is essential for a quantitative interpretation
of the data.Comment: 16 pages, 14 figure
A chiral crystal in cold QCD matter at intermediate densities?
The analogue of Overhauser (particle-hole) pairing in electronic systems
(spin-density waves with non-zero total momentum ) is analyzed in
finite-density QCD for 3 colors and 2 flavors, and compared to the
color-superconducting BCS ground state (particle-particle pairing, =0). The
calculations are based on effective nonperturbative four-fermion interactions
acting in both the scalar diquark as well as the scalar-isoscalar quark-hole
('') channel. Within the Nambu-Gorkov formalism we set up the coupled
channel problem including multiple chiral density wave formation, and evaluate
the resulting gaps and free energies. Employing medium-modified
instanton-induced 't Hooft interactions, as applicable around
GeV (or 4 times nuclear saturation density), we find the 'chiral crystal phase'
to be competitive with the color superconductor.Comment: 14 pages ReVTeX, including 11 ps-/eps-figure
Dileptons in High-Energy Heavy-Ion Collisions
The current status of our understanding of dilepton production in
ultrarelativistic heavy-ion collisions is discussed with special emphasis on
signals from the (approach towards) chirally restored and deconfined phases. In
particular, recent results of the CERN-SPS low-energy runs are compared to
model predictions and interpreted. Prospects for RHIC experiments are given.Comment: Invited talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; 1 Latex and
9 eps-/ps-files Reoprt No.: SUNY-NTG-02-0
Hadro-Chemistry and Evolution of (Anti-) Baryon Densities at RHIC
The consequences of hadro-chemical freezeout for the subsequent hadron gas
evolution in central heavy-ion collisions at RHIC and LHC energies are
discussed with special emphasis on effects due to antibaryons. Contrary to
naive expectations, their individual conservation, as implied by experimental
data, has significant impact on the chemical off-equilibrium composition of
hadronic matter at collider energies. This may reflect on a variety of
observables including source sizes and dilepton spectra.Comment: 4 pages ReVTeX incl. 3 ps-figs, submitted to PR
Nuclear Saturation with in-Medium Meson Exchange Interactions
We show that the assumption of dropping meson masses together with
conventional many-body effects, implemented in the relativistic Dirac-Brueckner
formalism, explains nuclear saturation. We use a microscopic model for
correlated exchange and include the standard many-body effects on the
in-medium pion propagation, which initially increase the attractive
nucleon-nucleon () potential with density. For the vector meson exchanges
in both the and sector, we assume Brown-Rho scaling which---in
concert with `chiral' contact interactions---reduces the attraction at
higher densities.Comment: 5 pages REVTeX, 2 eps-figures included, submitted to Phys. Rev. Let
Isospin Fluctuations in QCD and Relativistic Heavy-Ion Collisions
We address the role of fluctuations in strongly interacting matter during the
dense stages of a heavy-ion collision through its electromagnetic emission.
Fluctuations of isospin charge are considered in a thermal system at rest as
well as in a moving hadronic fluid at fixed proper time within a finite bin of
pseudo-rapidity. In the former case, we use general thermodynamic relations to
establish a connection between fluctuations and the space-like screening limit
of the retarded photon self-energy, which directly relates to the emissivities
of dileptons and photons. Effects of hadronic interactions are highlighted
through two illustrative calculations. In the latter case, we show that a
finite time scale inherent in the evolution of a heavy-ion collision
implies that equilibrium fluctuations involve both space-like and time-like
components of the photon self-energy in the system. Our study of non-thermal
effects, explored here through a stochastic treatment, shows that an early and
large fluctuation in isospin survives only if it is accompanied by a large
temperature fluctuation at freeze-out, an unlikely scenario in hadronic phases
with large heat capacity. We point out prospects for the future which include:
(1) A determination of the Debye mass of the system at the dilute freeze-out
stage of a heavy-ion collision, and (2) A delineation of the role of charge
fluctuations during the dense stages of the collision through a study of
electromagnetic emissivities.Comment: 12 pages ReVTeX incl. 4 ps-fig
Thermal Photons in Strong Interactions
A brief survey is given on the current status of evaluating thermal
production of photons from a strongly interacting medium. Emphasis is put on
recent progress in assessing equilibrium emission rates in both hadronic and
quark-gluon matter. We also give an update on the status of comparing
theoretical calculations with experimental data from heavy-ion collisions at
the SPS, as well as prospects for RHIC. Finally, applications of photon rate
calculations to colorsuperconducting quark matter are discussed.Comment: Brief Review for Mod. Phys. Lett A, 15 pages latex incl. 12 ps/eps
figs and style file ws-mpla.cl
The Vector Probe in Heavy-Ion Reactions
We review essential elements in using the channel as a probe for
hot and dense matter as produced in (ultra-) relativistic collisions of heavy
nuclei. The uniqueness of the vector channel resides in the fact that it
directly couples to photons, both real and virtual (dileptons), enabling the
study of thermal radiation and in-medium effects on both light () and heavy () vector mesons. We emphasize the importance
of interrelations between photons and dileptons, and characterize relevant
energy/mass regimes through connections to Quark-Gluon-Plasma emission and
chiral symmetry restoration. Based on critical analysis of our current
understanding of data from fixed-target energies, we identify open key
questions to be addressed.Comment: Invited Talk at the Hot Quarks 2004 Workshop, July 18-24, 2004 (Taos
Valley, NM, USA), 15 pages latex incl 14 figs and iop style files, to appear
in the proceeding
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