1,382 research outputs found
Core-corona separation in the UrQMD hybrid model
We employ the UrQMD transport + hydrodynamics hybrid model to estimate the
effects of a separation of the hot equilibrated core and the dilute corona
created in high energy heavy ion collisions. It is shown that the fraction of
the system which can be regarded as an equilibrated fireball changes over a
wide range of energies. This has an impact especially on strange particle
abundancies. We show that such a core corona separation allows to improve the
description of strange particle ratios and flow as a function of beam energy as
well as strange particle yields as a function of centrality.Comment: 10 pages, 11 figures, version accepted by PR
Resonance Production in RHIC Collisions
Results of resonance particle production measured at RHIC in 200 GeV Au+Au collisions are compared to measurements in p+p and d+Au
collisions in order to verify the existence of an extended hardronically
interacting medium. Yield and momentum distributions of resonances maybe
modified during the fireball lifetime due to resonance decay and the subsequent
rescattering of their decay daughters as well as the regeneration of resonances
from their decay products. Modified momentum spectra in heavy ion collisions
may change the nuclear modification factor R. The influence on the
elliptic flow v due to late regeneration of resonances is discussed.Comment: 6 pages, 6 figures, Proceedings of the 22st Winter Workshop on
Nuclear Dynamics, San Diago, California, 12-18 March, 200
Hadronization conditions in relativistic nuclear collisions and the QCD pseudo-critical line
We compare the reconstructed hadronization conditions in relativistic nuclear
collisions in the nucleon-nucleon centre-of-mass energy range 4.7-2760 GeV in
terms of temperature and baryon-chemical potential with lattice QCD
calculations, by using hadronic multiplicities. We obtain hadronization
temperatures and baryon chemical potentials with a fit to measured
multiplicities by correcting for the effect of post-hadronization rescattering.
The post-hadronization modification factors are calculated by means of a
coupled hydrodynamical-transport model simulation under the same conditions of
approximate isothermal and isochemical decoupling as assumed in the statistical
hadronization model fits to the data. The fit quality is considerably better
than without rescattering corrections, as already found in previous work. The
curvature of the obtained "true" hadronization pseudo-critical line kappa is
found to be 0.0048 +- 0.0026, in agreement with lattice QCD estimates; the
pseudo-critical temperature at vanishing mu_B is found to be 164.3+-1.8 MeV.Comment: 9 pages, 2 figures. Minor corrections, version published in PL
Directed flow, a signal for the phase transition in Relativistic Nuclear Collisions?
The sign change of the slope of the directed flow of baryons has been
predicted as a signal for a first order phase transition within fluid dynamical
calculations. Recently, the directed flow of identified particles has been
measured by the STAR collaboration in the beam energy scan (BES) program. In
this article, we examine the collision energy dependence of directed flow
in fluid dynamical model descriptions of heavy ion collisions for
GeV. The first step is to reproduce the existing
predictions within pure fluid dynamical calculations. As a second step we
investigate the influence of the order of the phase transition on the
anisotropic flow within a state-of-the-art hybrid approach that describes other
global observables reasonably well. We find that, in the hybrid approach, there
seems to be no sensitivity of the directed flow on the equation of state and in
particular on the existence of a first order phase transition. In addition, we
explore more subtle sensitivities like e.g. the Cooper-Frye transition
criterion and discuss how momentum conservation and the definition of the event
plane affects the results. At this point, none of our calculations matches
qualitatively the behavior of the STAR data, the values of the slopes are
always larger than in the data.Comment: 7 pages, 7 figure
Dileptons in a coarse-grained transport approach
We calculate dilepton spectra in heavy-ion collisions using a coarse-graining
approach to the simulation of the created medium with the UrQMD transport
model. This enables the use of dilepton-production rates evaluated in
equilibrium quantum-field theory at finite temperatures and chemical
potentials.Comment: 4 pages, 2 figures, contribution to the proceedings of "The 15th
International Conference on Strangeness in Quark Matter" (SQM 2015), 06-11
July in Dubna, Russi
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