66 research outputs found
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
Estimation of the shear viscosity at finite net-baryon density from A+A collision data at GeV
Hybrid approaches based on relativistic hydrodynamics and transport theory
have been successfully applied for many years for the dynamical description of
heavy ion collisions at ultrarelativistic energies. In this work a new viscous
hybrid model employing the hadron transport approach UrQMD for the early and
late non-equilibrium stages of the reaction, and 3+1 dimensional viscous
hydrodynamics for the hot and dense quark-gluon plasma stage is introduced.
This approach includes the equation of motion for finite baryon number, and
employs an equation of state with finite net-baryon density to allow for
calculations in a large range of beam energies. The parameter space of the
model is explored, and constrained by comparison with the experimental data for
bulk observables from SPS and the phase I beam energy scan at RHIC. The favored
parameter values depend on energy, but allow to extract the effective value of
the shear viscosity coefficient over entropy density ratio in the
fluid phase for the whole energy region under investigation. The estimated
value of increases with decreasing collision energy, which may
indicate that of the quark-gluon plasma depends on baryochemical
potential .Comment: minor changes in the text, results for constant eta*T/w added.
Version accepted for publication in Phys. Rev.
Hadronic and electromagnetic probes of hot and dense matter in a Boltzmann+Hydrodynamics model of relativistic nuclear collisions
We present recent results on bulk observables and electromagnetic probes
obtained using a hybrid approach based on the Ultrarelativistic Quantum
Molecular Dynamics transport model with an intermediate hydrodynamic stage for
the description of heavy-ion collisions at AGS, SPS and RHIC energies. After
briefly reviewing the main results for particle multiplicities, elliptic flow,
transverse momentum and rapidity spectra, we focus on photon and dilepton
emission from hot and dense hadronic matter.Comment: To appear in the proceedings of WISH 2010: International Workshop on
Interplay between Soft and Hard interactions in particle production at
ultrarelativistic energies, Catania, Italy, 8-10 September 201
Centrality and Energy Dependence of Proton, Light Fragment and Hyperon Production
Recent results of the NA49 collaboration are discussed. These include the
energy dependence of stopping and the production of the light fragments t and
3He. New data on the system size dependence of hyperon production at 40A and
158AGeV are also presented.Comment: 4 pages, Quark Matter 2006 proceeding
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