H. Sorge

Relativistic quantum molecular dynamics approach to nuclear collisions at ultrarelativistic energies

Abstract A Lorentz invariant extension of the well-known quantum molecular dynamics approach is employed to investigate the space-time evolution of heavy ion collision at Dubna, AGS and CERN energies ( E kin = 3A GeV …200 AGeV ). The model combines multiple twobody elastic and inelastic scattering plus soft many body potential interactions. The predicted multiplicity and rapidity distributions, transverse energy production and flow effects compare well with the experimental data at these energies. Predictions to the stopping power at the AGS-Booster are also presented. The RQMD results demonstrate the importance of nuclear stopping and secondary scattering up to the highest beam energies currently available. This is of particular importance for the recently observed enhancement of strangeness production compared to pp data, which was proposed as a signal for quark gluon plasma formation.

Colour rope formation and strange baryon production in ultrarelativistic heavy ion collisions

Abstract Enhanced strangenees production in recent experiments with S projectiles on different targets at a beam energy of 200 A GeV has been reported by several experimental groups (NA35, WA85, NA34). Here we consider that elementary triplet colour charges which are excited in the initial stage of a nucleus-nucleus collision may combine forming highly “ropes”. The colour ropes decay by quark-antiquark pair creation creation screening the initial field. We implemented the generated and decay of ropes into a new version of the Monte Carlo program RQMD which is based on string excitation in ultrarelativistic nucleus-nucleus collisions. We find that all measured strange particle yields in S+S can be quantitatively understood employing the rope mechanism in addition to hadronic rescattering.

φ meson production in ultrarelativistic heavy ion collisions

Abstract The production of φ mesons is studied in the framework of relativistic quantum molecular dynamics. We analyze the contributing sources and find that strong chromoelectric fields from string fusion ( color ropes ) and hadronic rescattering enhance the φ yield in central S (200 A GeV) + U collisions considerably. RQMD predicts different scaling of vector meson ( φ , ϱ 0 and ω ) decay yields with atomic mass numbers of the colliding system. The calculations give a factor of two enhancement of φ and ϱ 0 versus of forty percent suppression of ω decays in S + U , if normalized on pion multiplicity and compared to pp reactions at the same energy. The calculated double ratio of φ / ϱ 0 + ω decays in the dimuon channel for S + U and p + p / W reactions compares well with recent measurements from the NA38 and HELIOS/3 collaborations at CERN.

Testing transport theories with correlation measurements

Abstract Two-particle correlations offer the best chance to view the space-time evolution of relativistic heavy-ion collisions. After reviewing motivations for measuring two-particle correlation functions, predictions of two-particle correlations using full-event simulations are compared to experimental results. Several conclusions regarding space-time evolution of a reaction are reached.

VUU and (R)QMD model of high energy heavy ion collisions

Abstract The Vlasov Uehling Uhlenbeck (VUU)-model, the Quantum Molecular Dynamics (QMD) and its covariant extension, the Relativistic Quantum Molecular Dynamics (RQMD) are used to investigate the formation of baryon rich nuclear matter in heavy ion collisions over a wide range of bombarding energy from several hundred MeV/nucleon to several hundred GeV/nucleon. Stopping and bounce off are predicted at all energies if heavy systems are investigated. The formation of Δ-matter is predicted at E > 1GeV/nucleon in the baryon rich region, this is supported by the yields and spectra of pions and is manifested by the enhancement of low pT pions. (Anti)-strangeness is created copiously leading to larger kaon and lambda yields. This together with the large baryon densities facilitates the formation of multi hypernuclei and droplets of strange quark matter, so-called strangelets.

Collective effects and nuclear stopping

One of the most interesting challenges of modern heavy ion physics is the extraction of the equation of state for excited and ultra dense nuclear matter. The temperatures and densities of a possible phase transition to colour deconfinement (quark-gluon plasma) or restored chiral symmetry might, be extracted from observables which are sensitive to collective behaviour. In this paper we give examples for such kind of collective effects and try to point out possible observables for their measurement. We shall focus on:

Dielectron production in pp and pA collisions at 4.9 GeV

Abstract A covariant phase space approach (RQMD) is used to predict dielectron mass spectra for interactions of proton on proton and proton on deuteron at 4.9 GeV incident energy. Dalitz decays of ηs dominate the dilepton mass spectra above the π0 mass up to 0.5 GeV while decays of vector mesons produce a peak around the ρ0 mass. pn bremsstrahlung is strongly reduced at these masses. This is due to the forward peak in the differential elastic cross section d σ d t at energies above Ekin≈1 GeV, as compared to previous calculations. The results for p+Be at 4.9 GeV compare well with available DLS-data.

Mass dependence of hadron distributions in ultrarelativistic nucleus-nucleus collisions

Abstract(Anti-) baryon and kaon distributions in nucleus-nucleus reactions at 200 AGeV are studied in the framework of the transport model RQMD. Production mechanisms for strangeness and baryon pairs are tested by comparing their projectile and target mass dependence to available experimental data. RQMD contains two collective production processes, fusion of overlapping strings into highly charged chromoelectric ropes and hadronic rescattering. It turns out that both rope formation and hadronic rescattering are of importance for creation-and annihilation-of strangeness and antibaryons.

Strange particle production in proton-nucleus reactions at ultrarelativistic energies

AbstractEnhanced yields of lambdas and other strange hadrons in experiments on nuclear targets at incident energies of 200 GeV have been recently reported by several experimental groups. We calculated events for proton projectiles on different targets in the framework of the relativistic quantum molecular dynamics approach which is based on string excitation and fragmentation with subsequent hadronic collisions. Here we address the question whether the experimentally found lambda enhancement in hadron-nucleus collisions can be understood by interactions of secondary hadrons formed in the target nucleus. Our results for Λs, kaons and