Remnants of Initial Anisotropic High Energy Density Domains in Nucleus-Nucleus Collisions

Anisotropic high energy density domains may be formed at early stages of ultrarelativistic heavy ion collisions, e.g. due to phase transition dynamics or non-equilibrium phenomena like (mini-)jets. Here we investigate hadronic observables resulting from an initially created anisotropic high energy density domain. Based on our studies using a transport model we find that the initial anisotropies are reflected in the freeze-out multiplicity distribution of both pions and kaons due to secondary hadronic rescattering. The anisotropy appears to be stronger for particles at high transverse momenta. The overall kaon multiplicity increases with large fluctuations of local energy densities, while no change has been found in the pion multiplicity.Comment: Submitted to PR

Elliptical flow -- a signature for early pressure in ultrarelativistic nucleus-nucleus collisions

Elliptical energy flow patterns in non-central Au(11.7AGeV) on Au reactions have been studied employing the RQMD model. The strength of these azimuthal asymmetries is calculated comparing the results in two different modes of RQMD (mean field and cascade). It is found that the elliptical flow which is readily observable with current experimental detectors may help to distinguish different reasonable expansion scenarios for baryon-dense matter. The final asymmetries are very sensitive to the pressure at maximum compression, because they involve a partial cancelation between early squeeze-out and subsequent flow in the reaction plane. This cancelation can be expected to occur in a broad energy region covered by the current heavy ion fixed-target programs at BNL and at CERN.Comment: 14 pages LaTeX including 3 postscript figure

Pion chemical equilibration in heavy ion collisions : relativistic quantum molecular dynamic analysis

In the framework of relativistic quantum molecular dynamics the authors find that the pion system produced in central heavy-ion collisions at Elab/A approximately 1 GeV/nucl. is out of chemical equilibrium. Pion chemical potential is large and decreases during the expansion stage

Evidence of early multi-strange hadron freeze-out in high energy nuclear collisions

Recently reported transverse momentum distributions of strange hadrons produced in Pb(158AGeV) on Pb collisions and corresponding results from the relativistic quantum molecular dynamics (RQMD) approach are examined. We argue that the experimental observations favor a scenario in which multi-strange hadrons are formed and decouple from the system rather early at large energy densities (around 1 GeV/fm$^3$). The systematics of the strange and non-strange particle spectra indicate that the observed transverse flow develops mainly in the late hadronic stages of these reactions.Comment: 4 pages, 4 figure

Systematic Study of the Kaon to Pion Multiplicity Ratios in Heavy-Ion Collisions

We present a systematic study of the kaon to pion multiplicity ratios (K+/pi+ and K-/pi-) in heavy-ion collisions from AGS to RHIC energy using the Relativistic Quantum Molecular Dynamics (RQMD) model. The model satisfactorily describes the available experimental data on K+/pi+ and K-/pi-. Within the model, we find that the strong increase of the ratios with the number of participants is mainly due to hadronic rescattering of produced mesons with ingoing baryons and their resonances. The enhancement of K/pi in heavy-ion collisions with respect to elementary p+p interactions is larger at AGS energy than SPS energy, and decreases smoothly with bombarding energy. The total multiplicity ratios at RHIC energy are predicted by RQMD to be K+/pi+ = 0.19 and K-/pi- = 0.15.Comment: 10 pages, 8 figures, RevTeX style. A section is added to discuss effects of rope formatio

On the Equation of State of Nuclear Matter in 158A GeV Pb+Pb Collisions

Within a hydrodynamical approach we investigate the sensitivity of single inclusive momentum spectra of hadrons in 158A GeV Pb+Pb collisions to three different equations of state of nuclear matter. Two of the equations of state are based on lattice QCD results and include a phase transition to a quark-gluon plasma. The third equation of state has been extracted from the microscopic transport code RQMD under the assumption of complete local thermalization. All three equations of state provide reasonable fits to data taken by the NA44 and NA49 Collaborations. The initial conditions before the evolution of the fireballs and the space-time evolution pictures differ dramatically for the three equations of state when the same freeze-out temperature is used in all calculations. However, the softest of the equations of state results in transverse mass spectra that are too steep in the central rapidity region. We conclude that the transverse particle momenta are determined by the effective softness of the equation of state during the fireball expansion.Comment: 4 pages, including 4 figures and 2 tables. For a PostScript file of the manuscript, you can also goto http://t2.lanl.gov/schlei/eprint.htm

A stopped Delta-Matter Source in Heavy Ion Collisions at 10 GeV/n

We predict the formation of highly dense baryon-rich resonance matter in Au+Au collisions at AGS energies. The final pion yields show observable signs for resonance matter. The Delta(1232) resonance is predicted to be the dominant source for pions of small transverse momenta. Rescattering effects -- consecutive excitation and deexcitation of Deltas -- lead to a long apparent lifetime (> 10 fm/c) and rather large volumina (several 100 fm^3) of the Delta-matter state. Heavier baryon resonances prove to be crucial for reaction dynamics and particle production at AGS.Comment: 17 pages, 5 postscript figures, uses psfig.sty and revtex.st

Inhomogeneous Nucleation of Quark-Gluon Plasma in High Energy Nuclear Collisions

We estimate the probability that a hard nucleon-nucleon collision is able to nucleate a seed of quark--gluon plasma in the surrounding hot and dense hadronic matter formed during a central collision of two large nuclei at AGS energies. The probability of producing at least one such seed is on the order of 1-100\%. We investigate the influence of quark--gluon plasma formation on the observed multiplicity distribution and find that it may lead to noticable structure in the form of a bump or shoulder.Comment: 16 pages, latex and 12 ps figures available on reques

Antibaryons in massive heavy ion reactions: Importance of potentials

In the framework of RQMD we investigate antiproton observables in massive heavy ion collisions at AGS energies and compare to preliminary results of the E878 collaboration. We focus here on the considerable influence of the *real* part of an antinucleon--nucleus optical potential on the antiproton momentum spectra

Analysis of hadron production in nucleus-nucleus interactions up to and out of kinematical limit of free NN-collisions in the frame of FRITIOF model

In the framework of the modified FRITIOF model, the inclusive spectra of the cumulative $\pi ^0$-, $\pi ^-$-mesons and protons produced in the nucleus-nucleus interactions at 4.5 GeV/c/nucleon and 4.2 GeV/c/nucleon are calculated. It is shown that the model reproduces qualitatively, and in some cases quantitatively the main experimental regularities of $\pi$-mesons production, and "soft" part of the proton spectra. According to the model the production of the cumulative particles is connected with the mechanism of the "soft" nucleon-nucleon interaction.Comment: 12 pages, 11 figure