828 research outputs found
Density Perturbations in Heavy-Ion Collisions below the Critical Point
Heavy ion collisions at large baryon density may exhibit a first order phase
transition from a chirally symmetric phase to the symmetry broken ground state.
This should then lead to large density inhomogeneities, which affect the
relative hadron multiplicities.Comment: 1 page, 1 figure, contribution to the GSI annual report 200
Hadron yields from thermalized minijets at RHIC and LHC
We calculate the yields of pions, kaons, and -mesons for RHIC and LHC
energies assuming thermodynamical equilibration of the produced minijets, and
using as input results from pQCD for the energy densities at midrapidity. In
the calculation of the production of partons and of transverse energy one has
to account for nuclear shadowing. By using two parametrizations for the gluon
shadowing one derives energy densities differing strongly in magnitude. In this
publication we link those perturbatively calculated energy densities of partons
via entropy conservation in an ideal fluid to the hadron multiplicities at
chemical freeze-out.Comment: Talk given at the International Europhysics Conference on High Energy
Physics, EPS-HEP99, Tampere, Finland, July 1999, 3 page
In-medium vector meson masses in a Chiral SU(3) model
A significant drop of the vector meson masses in nuclear matter is observed
in a chiral SU(3) model due to the effects of the baryon Dirac sea. This is
taken into account through the summation of baryonic tadpole diagrams in the
relativistic Hartree approximation. The appreciable decrease of the in-medium
vector meson masses is due to the vacuum polarisation effects from the nucleon
sector and is not observed in the mean field approximation.Comment: 26 pages including 10 figures; the text has been modified for clarit
Transport calculation of dilepton production at ultrarelativistic energies
Dilepton spectra are calculated within the microscopic transport model UrQMD
and compared to data from the CERES experiment. The invariant mass spectra in
the region 300 MeV < M < 600 MeV depend strongly on the mass dependence of the
meson decay width which is not sufficiently determined by the Vector
Meson Dominance model. A consistent explanation of both the recent Pb+Au data
and the proton induced data can be given without additional medium effects
Entropy Production in Collisions of Relativistic Heavy Ions -- a signal for Quark-Gluon Plasma phase transition?
Entropy production in the compression stage of heavy ion collisions is
discussed within three distinct macroscopic models (i.e. generalized RHTA,
geometrical overlap model and three-fluid hydrodynamics). We find that within
these models \sim 80% or more of the experimentally observed final-state
entropy is created in the early stage. It is thus likely followed by a nearly
isentropic expansion. We employ an equation of state with a first-order phase
transition. For low net baryon density, the entropy density exhibits a jump at
the phase boundary. However, the excitation function of the specific entropy
per net baryon, S/A, does not reflect this jump. This is due to the fact that
for final states (of the compression) in the mixed phase, the baryon density
\rho_B increases with \sqrt{s}, but not the temperature T. Calculations within
the three-fluid model show that a large fraction of the entropy is produced by
nuclear shockwaves in the projectile and target. With increasing beam energy,
this fraction of S/A decreases. At \sqrt{s}=20 AGeV it is on the order of the
entropy of the newly produced particles around midrapidity. Hadron ratios are
calculated for the entropy values produced initially at beam energies from 2 to
200 AGeV.Comment: 17 pages, 8 figures, uses epsfig.sty; Submitted to Nucl.Phys.
Hypernuclei, dibaryon and antinuclei production in high energy heavy ion collisions: Thermal production vs. Coalescence
We study the production of (hyper-)nuclei and di-baryons in most central
heavy Ion collisions at energies of GeV. In particular we are
interested in clusters produced from the hot and dense fireball. The formation
rate of strange and non-strange clusters is estimated by assuming thermal
production from the intermediate phase of the UrQMD-hydro hybrid model and
alternatively by the coalescence mechanism from a hadronic cascade model. Both
model types are compared in detail. For most energies we find that both
approaches agree in their predictions for the yields of the clusters. Only for
very low beam energies, and for di-baryons including 's, we observe
considerable differences. We also study the production of anti-matter clusters
up to top RHIC energies and show that the observation of anti- and even
anti- is feasible. We have found a considerable qualitative
difference in the energy dependence of the strangeness population factor
when comparing the thermal production with the coalescence results.Comment: 9 pages, 8 figures and 2 tables, version accepted by PL
Open-charm enhancement at FAIR?
We have calculated the D-meson spectral density at finite temperature within
a self-consistent coupled-channel approach that generates dynamically the
(2593) resonance. We find a small mass shift for the D-meson in
this hot and dense medium while the spectral density develops a sizeable width.
The reduced attraction felt by the D-meson in hot and dense matter together
with the large width observed have important consequences for the D-meson
production in the future CBM experiment at FAIR.Comment: 4 pages, 2 figures, to appear in the proceedings of 9th International
Conference on Strangeness in Quark Matter (SQM2006), Los Angeles, USA, March
26-31, 200
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