J. Konopka

Microscopic models for ultrarelativistic heavy ion collisions

In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended collision term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from

Modelling the many-body dynamics of heavy ion collisions : present status and future perspective

E_{lab} 200

Equation of State, Spectra and Composition of Hot and Dense Infinite Hadronic Matter in a Microscopic Transport Model ∗

GeV/nucleon, allowing for a consistent calculation of excitation functions from the intermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

ARE WE CLOSE TO AN EQUILIBRATED QUARK-GLUON PLASMA? NONEQUILIBRIUM ANALYSIS OF PARTICLE PRODUCTION IN ULTRARELATIVISTIC HEAVY ION COLLISIONS

Abstract: Basic problems of the semiclassical microscopic modelling of strongly interacting systems are discussed within the framework of Quantum Molecular Dynamics (QMD). This model allows to study the influence of several types of nucleonic interactions on a large variety of observables and phenomena occurring in heavy ion collisions at relativistic energies. It is shown that the same predictions can be obtained with several – numerically completely different and independently written – programs as far as the same model parameters are employed and the same basic approximations are made. Many observables are robust against variations of the details of the model assumptions used. Some of the physical results, however, depend also on rather technical parameters like the preparation of the initial configuration in phase space. This crucial problem is connected with the description of the ground state of single nuclei, which differs among the various approaches. An outlook to an improved molecular dynamics scheme for heavy ion collisions is given.

Microscopic calculations of stopping, flow and electromagnetic radiation from 160AMeV to 160AGeV☆

Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine(February 9, 2008)Equilibrium properties of infinite relativistic hadron matter are investi-gated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD)model. The simulations are performed in a box with periodic boundary con-ditions. Equilibration times depend critically on energy and baryon densities.Energy spectra of various hadronic species are shown to be isotropic andconsistent with a single temperature in equilibrium. The variation of energydensity versus temperature shows a Hagedorn-like behavior with a limitingtemperature of 130±10 MeV. Comparison of abundances of different particlespecies to ideal hadron gas model predictions show good agreement only ifdetailed balance is implemented for all channels. At low energy densities,high mass resonances are not relevant; however, their importance raises withincreasing energy density. The relevance of these different conceptual frame-works for any interpretation of experimental data is questioned.

On the impossibility of temperature extraction from heavy ion induced particle spectra

Ratios of hadronic abundances are analyzed for pp and nucleus-nucleus collisions at sqrt(s)=20 GeV using the microscopic transport model UrQMD. Secondary interactions significantly change the primordial hadronic cocktail of the system. A comparison to data shows a strong dependence on rapidity. Without assuming thermal and chemical equilibrium, predicted hadron yields and ratios agree with many of the data, the few observed discrepancies are discussed.

Physics opportunities at RHIC and LHC

Abstract The behavior of hadronic matter at high baryon densities is studied within Ultrarelativistic Quantum Molecular Dynamics (UQMD). Baryonic stopping is observed for Au+Au collisions from SIS up to SPS energies. The excitation function of flow shows strong sensitivities to the underlying equation of state (EOS), allowing for systematic studies of the EOS. Effects of a density dependent pole of the ϱ-meson propagator on dilepton spectra are studied for different systems and centralities at CERN energies.

Hadrochemical vs. Microscopic Analysis of Particle Production and Freeze-Out in Ultrarelativistic Heavy Ion Collisions

Abstract Spectra of various particle species have been calculated with the Quantum Molecular Dynamics (QMD) prescription of very central collisions of Au+Au. They are compatible with the idea of a fully stopped thermal source which exhibits an exclusively transversal expansion beside the trivial one of an ideal gas. However, the microscopic analyses of the local flow velocities and temperatures indicate much lower temperatures at densities associated with the freeze-out. These results express the overall impossibility of a model-independent determination of nuclear temperatures from heavy ion spectral data.

Nuclear Cluster Equation of State

Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models—although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles)—all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Ψ meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from dat...

Treatment of fermions in microscopic models

The investigation of hot and dense nuclear matter in ultra-relativistic heavy-ion collisions in general1, 2, 3, and the search for a deconfinement phase transition from hadronic to quark matter in particular4, 5, 6, 7, is one of the currently fastest moving research fields of nuclear physics. Hadron abundances and ratios have been suggested as possible signatures for exotic states and phase transitions in dense nuclear matter. In addition they have been applied to study the degree of chemical equilibration in a relativistic heavy-ion reaction. Bulk properties like temperatures, entropies and chemical potentials of highly excited hadronic matter have been extracted assuming thermal and chemical equilibrium8, 9, 10, 11, 12, 13, 14.