We present a coupled Boltzmann and hydrodynamics approach to relativistic heavy ion reactions. This hybrid approach is based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. Event-by-event fluctuations are directly taken into account via the non-equilibrium initial conditions generated by the initial collisions and string fragmentations in the microscopic UrQMD model. After a (3+1)-dimensional ideal hydrodynamic evolution, the hydrodynamical fields are mapped to hadrons via the Cooper-Frye equation and the subsequent hadronic cascade calculation within UrQMD proceeds to incorporate the important final state effects for a realistic freeze-out. This implementation allows to compare pure microscopic transport calculations with hydrodynamic calculations using exactly the same initial conditions and freeze-out procedure. The effects of the change in the underlying dynamics -ideal fluid dynamics vs. non-equilibrium transport theory -will be explored. The freeze-out and initial state parameter dependences are investigated for different observables. Furthermore, the time evolution of the baryon density and particle yields are discussed. We find that the final pion and proton multiplicities are lower in the hybrid model calculation due to the isentropic hydrodynamic expansion while the yields for strange particles are enhanced due to the local equilibrium in the hydrodynamic evolution. The results of the different calculations for the mean transverse mass excitation function, rapidity and transverse mass spectra for different particle species at three different beam energies are discussed in the context of the available data.

A simple confining separable interaction Ansatz for the rainbow-ladder truncated QCD Dyson-Schwinger equations is used to implement chiral restoration and quark deconfinement in a study ofqq meson states at finite temperature. The model is fixed at T = 0 by reproducing selected π and ρ properties. Deconfinement and chiral restoration are found to both occur at Tc = 146 MeV. In the pion sector, we investigate Mπ(T ) and fπ(T ) along with the exact QCD mass relation and the GMOR relation. For the vector mode, we investigate the 3-space transverse and longitudinal masses M T ρ (T ) and M L ρ (T ), along with the width for the decay ρ 0 → e + e − . The equation of state (EOS) for the model is investigated in the T − µ plane, a tri-critical point is identified and the relationship to a bag model is discussed. The deconfinement transition in rapidly rotating neutron stars is considered and a new signal from the pulsar timing in binary systems with mass accretion is suggested. The model is used to discuss the possibility of a superconducting quark matter phase.

The pseudorapidity behaviour of the azimuthal anisotropy parameters v1 and v2 of inclusive charged (h ± ) hadrons and their dependence on the centrality has been studied in Au+Au collisions at full RHIC energy of √ sNN = 200 GeV within the microscopic quark-gluon string model. The QGSM simulation results for the directed flow v1 show antiflow alignment within the pseudorapidity range |η| ≤ 2 in a fair agreement with the experimental v1(η) data, but cannot reproduce the further development of the antiflow up to |η| ≈ 3.5. The η dependence of the elliptic flow v2 extracted from the simulations agrees well with the experimental data in the whole pseudorapidity range for different centrality classes. The centrality dependence of the integrated elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS experimental distribution. The transverse momentum dependence of the elliptic flow of identified (π ± , K ± , p,p) and inclusive charged hadrons is studied also. The model reproduces quantitatively the low-pT part of the distributions rather good, but underestimates the measured elliptic flow for transverse momenta pT > 1 GeV/c. Qualitatively, however, the model is able to reproduce the saturation of the v2(pT ) spectra with rising pT as well as the crossing of the elliptic flow for mesons and baryons.

The implications of parton recombination processes on the dynamics of ultrarelativistic heavy-ion reactions are investigated. To do so, the quark-gluon string transport model has been extended for partonic recombination and fusion processes. Parton recombination leads to short equilibration times and improves significantly on the theoretical description of measured directed and elliptic flow, i.e., v1 and v2, distributions in Au+Au collisions at √ sNN = 200 GeV, in particular what concerns their pseudorapidity dependence. The shape of v2(η) is found to be closely related to fast thermalization.

We investigate the in-medium modification of the charmonium break-up process due to the Mott effect for light (π) and open-charm (D, D * ) mesons at the chiral/deconfinement phase transition. A model calculation for the process J/ψ + π → D +D * +h.c. is presented which demonstrates that the Mott effect for the D-mesons leads to a threshold effect in the thermal averaged break-up cross section. This effect is suggested as an explanation of the phenomenon of anomalous J/ψ suppression in the CERN NA50 experiment.