Jan Steinheimer

Hadron formation in relativistic nuclear collisions and the QCD phase diagram.

We study particle production in ultrarelativistic nuclear collisions at CERN SPS and LHC energies and the conditions of chemical freeze-out. We determine the effect of the inelastic reactions between hadrons occurring after hadronization and before chemical freeze-out employing the ultrarelativistic quantum molecular dynamics hybrid model. The differences between the initial and the final hadronic multiplicities after the rescattering stage resemble the pattern of data deviation from the statistical equilibrium calculations. By taking these differences into account in the statistical model analysis of the data, we are able to reconstruct the original hadrochemical equilibrium points in the (T, μ(B)) plane which significantly differ from chemical freeze-out ones and closely follow the parton-hadron phase boundary recently predicted by lattice quantum chromodynamics.

Spinodal amplification of density fluctuations in fluid-dynamical simulations of relativistic nuclear collisions.

Extending a previously developed two-phase equation of state, we simulate head-on relativistic lead-lead collisions with fluid dynamics, augmented with a finite-range term, and study the effects of the phase structure on the evolution of the baryon density. For collision energies that bring the bulk of the system into the mechanically unstable spinodal region of the phase diagram, the density irregularities are being amplified significantly. The resulting density clumping may be exploited as a signal of the phase transition, possibly through an enhanced production of composite particles.

An effective chiral hadron–quark equation of state

Institut fur Theoretische Physik, Goethe-Universitat - Max-von-Laue-Str. 1--> - D-60438 - Frankfurt am Main - Germany (Steinheimer, J)We construct an effective model for the QCD equation of state, taking into account chiral symmetry restoration as well as the deconfinement phase transition. The correct asymptotic degrees of freedom at the high and low temperature limits are included (quarks

(3+1)-dimensional hydrodynamic expansion with a critical point from realistic initial conditions

\leftrightarrow

Heavy quark transport in heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider within the UrQMD hybrid model

hadrons). The model shows a rapid crossover for both order parameters, as is expected from lattice calculations. We then investigate the thermodynamic properties of the model at

Hadronic resonance production and interaction in partonic and hadronic matter in the EPOS3 model with and without the hadronic afterburner UrQMD

\mu_B=0

Examination of directed flow as a signal for a phase transition in relativistic nuclear collisions

. All thermodynamic quantities are in qualitative agreement with lattice data, while apparent quantitative differences can be attributed to hadronic contributions and excluded volume corrections.

Non-equilibrium phase transition in relativistic nuclear collisions: Importance of the equation of state

We investigate a (3+1)-dimensional hydrodynamic expansion of the hot and dense system created in head-on collisions of Pb+Pb/Au+Au at beam energies from 5 to 200 GeV/nucleon. An equation of state is used that incorporates a critical end point (CEP) in line with the lattice data. The necessary initial conditions for the hydrodynamic evolution are taken from a microscopic transport approach, the ultrarelativistic quantum molecular dynamics (UrQMD) model. We compare the properties of the initial state and the full hydrodynamic calculation with an isentropic expansion employing an initial state from a simple overlap model. We find that the specific entropies (S/A) from both initial conditions are very similar and only depend on the underlying equation of state. Using the chiral (hadronic) equation of state, we investigate the expansion paths for both initial conditions. Defining a critical area around the critical point, we show at what beam energies one can expect to have a sizable fraction of the system close to the critical point. Finally, we emphasize the importance of the equation of state of strongly interacting matter in the (experimental) search for the CEP.

Centrality dependence of hadronization and chemical freeze-out conditions in heavy ion collisions at

Abstract We have implemented a Langevin approach for the transport of heavy quarks in the UrQMD hybrid model. The UrQMD hybrid approach provides a realistic description of the background medium for the evolution of relativistic heavy ion collisions. We have used two different sets of drag and diffusion coefficients, one based on a T -Matrix approach and one based on a resonance model for the elastic scattering of heavy quarks within the medium. In case of the resonance model we have investigated the effects of different decoupling temperatures of the heavy quarks from the medium, ranging between 130 MeV and 180 MeV. We present calculations of the nuclear modification factor RAA, as well as of the elliptic flow v2 in Au+Au collisions at √ sNN = 200 GeV and Pb+Pb collisions at √ sNN = 2.76 TeV. To make our results comparable to experimental data at RHIC and LHC we have implemented a Peterson fragmentation and a quark coalescence approach followed by the semileptonic decay of the Dand B-mesons to electrons. We find that our results strongly depend on the decoupling temperature and the hadronization mechanism. At a decoupling temperature of 130 MeV we reach a good agreement with the measurements at both, RHIC and LHC energies, simultaneously for the elliptic flow v2 and the nuclear modification factor RAA.

\sqrt s_{NN}

We study the production of hadronic resonances and their interaction in the partonic and hadronic medium using the EPOS3 model, which employs the UrQMD model for the description of the hadronic phase. We investigate the centrality dependence of the yields and momentum distributions for various resonances (rho(770),K(892),phi(1020),Delta(1232),Sigma(1385),Lambda(1520),Xi(1530) and their antiparticles) in Pb-Pb collisions at sNN= 2.76 TeV. The predictions for K(892) and phi(1020) will be compared with the experimental data from the ALICE collaboration. The observed signal suppression of the K(892) with increasing centrality will be discussed with respect to the resonance interaction in the hadronic medium. The mean transverse momentum and other particle ratios such as phi(1020)/p and Omega/phi(1020) will be discussed with respect to additional contributions from the hadronic medium interactions.