FIAS Scientific Report 2010 - Frankfurt Institute for Advanced Studies ...

Research Report by Marcus Bleicher
Collaborators: M. Bleicher, E. Bratkovskaya, E. Santini, G. Moschelli, M. Hauer, B. Bäuchle, M. Nahrgang,
C. Herold, J. Steinheimer, G. Graef, V. Lindenstruth, J. Gerhard, H. Stöcker, I. Mishustin
These activites are supported by HIC for FAIR, EMMI, Helmholtz Association and GSI.
Hybrid+Boltzmann approach
A new modular hybrid transport approach was successfully developed and used to simulate heavy-ion reactions
in the FAIR/SPS energy domain. The model is based on the combination of a kinetic theory to describe the early
and late phase of the collision with an effective hydrodynamic model for the high density phase. It incorporates
a phase transition to the Quark Gluon Plasma (QGP) by means of different equations of state. The model was
used for several studies of QCD-Matter at FAIR energies. Among the observables studied were the production
of phi mesons and direct photons, Hanburry-Brown-Twiss correlations, event-by-event fluctuations and elliptic
flow of hadrons. New insights were gained by comparing the results of simulations with and without a phase
transition to a QGP. First studies were made to combine the hybrid model with a parton cascade.
Multi-particle interactions
Various techniques and implementations of multi-particle interactions have been performed within the Boltzmann
Approach to Multi-Particle Scattering (BAMPS) framework. A strong influence of the three-particle interactions
on the chemical equilibration times, the elliptic flow and the effective viscosity of the QCD medium
has been found. First steps towards an implementation of multi-particle interactions into the hadronic cascade
model Ultra-relativistic Quantum Molecular Dynamics (UrQMD) have been done. Here parton rearrangement
processes were implemented and the resulting effects were studied.
Modeling of the phase transition out of equilibrium
A new model to study fluctuations at the critical point was developed. It is based on the coupling of the chiral
field equations to hydrodynamic simulations. First studies have shown that the correlation length might be
shorter than previously expected because of a more realistic modeling of the collision dynamics.
Off-shell transport approach with quasi particles
A hybrid-transport model, Parton-Hadron-String Dynamics (PHSD) has been developed. It includes an equation
of state for the QGP adopted from lattice QCD calculations of the Bielefeld group. The basic idea is to
describe the properties of QCD adequately within the dynamical quasi-particle model (DQPM). In this case
the dressed propagator for quarks and gluons is given explicitly by means of complex self-energies. The latter
include a real part, which describes dynamical mass generation as well as an imaginary part for the interaction
rate of the effective degrees of freedom. The time-like part of the eight-dimensional distribution functions can
be propagated within the light-cone using off-shell transport theory once the self-energies have been fixed in
the DQPM. The hadronization process is described by means of Lorentz invariant transition rates based on
Kadanoff-Baym dynamics. Applications to relativistic nucleus-nucleus collisions in the FAIR and SPS energy
regime have been carried out.
Related publications in 2010:
1) E. Mount, G. Gräf, M. Mitrovski, M. Bleicher, M. Lisa: Correspondence between HBT radii and the emission
zone in non-central heavy ion collisions, [arXiv:1012.5941]
2) F. Wang, M. Bleicher: Nuclear absorption effects on Lambda-bar/p-bar ratio in heavy ion collisions,
[arXiv:1011.4289]
3) M. Nahrgang, M. Bleicher: Non-equilibrium fluctuations at the QCD phase transition, [arXiv:1011.5379]
4) K. Werner, Iu. Karpenko, T. Pierog, M. Bleicher, K. Mikhailov: Evidence for Hydrodynamic Evolution in
Proton-Proton Scattering at LHC Energies, [arXiv:1010.0400]
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