20 research outputs found
Dileptons and Photons from Coarse-Grained Microscopic Dynamics and Hydrodynamics Compared to Experimental Data
Radiation of dileptons and photons from high energy nuclear collisions
provides information on the space-time evolution of the hot dense matter
produced therein. We compute this radiation using relativistic hydrodynamics
and a coarse-grained version of the microscopic event generator UrQMD, both of
which provide a good description of the hadron spectra. The currently most
accurate dilepton and photon emission rates from perturbative QCD and from
experimentally-based hadronic calculations are used. Comparisons are made to
data on central Pb-Pb and Pb-Au collisions taken at the CERN SPS at a beam
energy of 158 A GeV. Both hydrodynamics and UrQMD provide very good
descriptions of the photon transverse momentum spectrum measured between 1 and
4 GeV, but slightly underestimate the low mass spectrum of e+e- pairs, even
with greatly broadened rho and omega vector mesons. Predictions are given for
the transverse momentum distribution of dileptons.Comment: 35 pages, 17 figure
Quasi-Particle Theory of Shear and Bulk Viscosities of Hadronic Matter
A theoretical framework for the calculation of shear and bulk viscosities of
hadronic matter at finite temperature is presented. The framework is based on
the quasi-particle picture. It allows for an arbitrary number of hadron species
with point-like interactions, and allows for both elastic and inelastic
collisions. Detailed balance is ensured. The particles have temperature
dependent masses arising from mean field or potential effects, which maintains
self-consistency between the equation of state and the transport coefficients.
As an example, we calculate the shear and bulk viscosity in the linear
model. The ratio of shear viscosity to entropy density shows a minimum in the
vicinity of a rapid crossover transition, while the ratio of bulk viscosity to
entropy density shows a maximum.Comment: 45 page
Emission of thermal photons and the equilibration time in Heavy-Ion collisions
The emission of hard real photons from thermalized expanding hadronic matter
is dominated by the initial high-temperature expansion phase. Therefore, a
measurement of photon emission in ultrarelativistic heavy-ion collisions
provides valuable insights into the early conditions realized in such a
collision. In particular, the initial temperature of the expanding fireball or
equivalently the equilibration time of the strongly interacting matter are of
great interest. An accurate determination of these quantities could help to
answer the question whether or not partonic matter (the quark gluon plasma) is
created in such collisions. In this work, we investigate the emission of real
photons using a model which is based on the thermodynamics of QCD matter and
which has been shown to reproduce a large variety of other observables. With
the fireball evolution fixed beforehand, we are able to extract limits for the
equilibration time by a comparison with photon emission data measured by WA98.Comment: 12 pages, 5 figures, accepted for publication at Phys. Rev.
A Family of Equations of State Based on Lattice QCD: Impact on Flow in Ultrarelativistic Heavy-Ion Collisions
We construct a family of equations of state within a quasiparticle model by
relating pressure, energy density, baryon density and susceptibilities adjusted
to first-principles lattice QCD calculations. The relation between pressure and
energy density from lattice QCD is surprisingly insensitive to details of the
simulations. Effects from different lattice actions, quark masses and lattice
spacings used in the simulations show up mostly in the quark-hadron phase
transition region which we bridge over by a set of interpolations to a hadron
resonance gas equation of state. Within our optimized quasiparticle model we
then examine the equation of state along isentropic expansion trajectories at
small net baryon densities, as relevant for experiments and hydrodynamic
simulations at RHIC and LHC energies. We illustrate its impact on azimuthal
flow anisotropies and transverse momentum spectra of various hadron species
Strangeness Report
The paper provides a short report on strangeness production in
ultrarelativistic nucleus-nucleus collision, with the main stress on strange
particle abundances.Comment: Proceedings of Quark Matter 200
Hydrodynamical Description of 200 A GeV/c S+Au Collisions: Hadron and Electromagnetic Spectra
We study relativistic S+Au collisions at 200 A GeV/c using a hydrodynamical
approach. We test various equations of state (EOSs), which are used to describe
the strongly interacting matter at densities attainable in the CERN-SPS heavy
ion experiments. For each EOS, suitable initial conditions can be determined to
reproduce the experimental hadron spectra; this emphasizes the ambiguity
between the initial conditions and the EOS in such an approach. Simultaneously,
we calculate the resulting thermal photon and dielectron spectra, and compare
with experiments. If one allows the excitation of resonance states with
increasing temperature, the electro-magnetic signals from scenarios with and
without phase transition are very similar and are not resolvable within the
current experimental resolution. With regard to the CERES dilepton data, none
of the EOSs considered, in conjunction with the standard leading order dilepton
rates, succeed in reproducing the observed excess of dileptons below the rho
peak. Our work, however, suggests that an improved measurement of the photon
and dilepton spectra has the potential to strongly constrain the EOS.Comment: Uses REVTeX, 48 pages, 13 Postscript figure
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
The QCD confinement transition: hadron formation
We review the foundations and the applications of the statistical and the
quark recombination model as hadronization models.Comment: 45 pages, 16 figures, accepted for publication in Landolt-Boernstein
Volume 1-23
Signatures of Quark-Gluon-Plasma formation in high energy heavy-ion collisions: A critical review
A critical review on signatures of Quark-Gluon-Plasma formation is given and
the current (1998) experimental status is discussed. After giving an
introduction to the properties of QCD matter in both, equilibrium- and
non-equilibrium theories, we focus on observables which may yield experimental
evidence for QGP formation. For each individual observable the discussion is
divided into three sections: first the connection between the respective
observable and QGP formation in terms of the underlying theoretical concepts is
given, then the relevant experimental results are reviewed and finally the
current status concerning the interpretation of both, theory and experiment, is
discussed. A comprehensive summary including an outlook towards RHIC is given
in the final section.Comment: Topical review, submitted to Journal of Physics G: 68 pages,
including 39 figures (revised version: only minor modifications, some
references added
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe