R. Mattiello

Energy density, stopping and flow in 10−20 A GeV heavy ion collisions

Abstract The Lorentz invariant molecular dynamics approach (RQMD) is employed to investigate the space-time evolution of heavy ion collisions at AGS energies ( E kin =10 A −;15 A GeV). The calculations for various nucleus nucleus reactions at AGS energies show a high degree of stopping power. The importance of secondary rescattering at these beam energies is demonstrated. The computed nucleon rapidity distributions are compared to available experimental data. It is demonstrated that nonlinear, collective effects like full stopping of target and projectile and matter flow could be expected for heavy projectiles only. For nuclear collisions in the Booster era at BNL we predict a stimulating future: Then a nearly equilibrated, long lived (8 fm/ c ) “macroscopic” volume of very high energy density (> 1 GeV/fm 3 ) and baryon density (> 5 times ground state density) is produced.

Meson production in pA and AA collisions at AGS energies

Abstract In the framework of the relativistic molecular dynamics approach (RQMD) we study pion and kaon production in the reactions p + Be, p + Au and Si + Au at a beam energy of 14.5 A GeV. In general we find good agreement for various particle yields and their momentum distributions comparing our results with recent experimental data taken at the AGS. In case of the gold target most of the primarily produced particles leave the reaction zone only after multiple interactions with the surrounding medium. For central Si on Au collisions meson and baryon resonance annihilation leads to strong strangeness enrichment. We predict that in effect of the meson cascading roughly half of the final pions are products from delta decays. This can be checked experimentally because of their characteristic momentum distribution.

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.

String dynamics in hadronic matter

Hadron production in soft hadronic collisions is successfully described by a longitudinal excitation and subsequent decay of color flux tubes. We consider the dynamics of interacting unstable strings as a generalization designed forhA andAA interactions at ultrarelativistic energies. The constituent quarks at the ends of the decaying strings and the produced hadrons can interact with the surrounding matter. The effect of secondary interactions in molecular dynamics calculations forAA collisions at CERN energies (200A GeV) can be seen in an enhancement of transverse energy, particle production and the mean transverse momenta. The results agree very well with the experimental measurements at ultrarelativistic beam energies inpp, hA and the recentAA collisions.

Is collective pion flow anticorrelated to nucleon flow

Abstract The in-plane transverse momentum of pions in Ne(2A GeV)Pb and Au(2A GeV)Au collisions is analysed in the framework of the Vlasov-Uehling-Uhlenbeck model. The rapidity dependence of pion flow shows the opposite sign as the nucleon flow. The anticorrelation of pions and nucleons can be explained by multiple πN scattering. It turns out that the nonzero transverse momentum for pions at target rapidities is no proof for pion absorption in contrast to claims in previous works. Pion absorption does not influence the angular distribution of pions but plays an important role for the absolute numbers of produced pions.

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.

Baryon stopping, flow and equilibration in ultrarelativistic heavy ion collisions

Abstract The Lorentz invariant molecular dynamics approach (RQMD) is employed to investigate the space-time evolution of heavy ion collisions at energies ( E kin = 10AGeV …200 AAGeV). The calculations for various nucleus nucleus reactions show a high degree of stopping power, almost independent from the incident beam energy. The importance of secondary rescattering at these beam energies is demonstrated. The computed nucleon rapidity distributions are compared to available experimental data. It is demonstrated that nonlinear, collective effects like full stopping of target and projectile and matter flow could be expected for heavy projectiles only. For nuclear collisions in the Booster era at BNL and for the lead beam at CERN SPS we predict a stimulating future: Then a nearly equilibrated, long lived (8 fm / c ) “macroscopic” volume of very high energy density (> 1 GeV / fm 3 ) and baryon density (> 5 times ground state density) is produced.

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:

Antibaryons in massive heavy ion reactions: Importance of potentials

In the framework of relativistic quantum molecular dynamics we investigate antiproton observables in massive heavy ion collisions at alternating-gradient synchrotron 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 p\ifmmode\bar\else\textasciimacron\fi{} momentum spectra. \textcopyright{} 1996 The American Physical Society.

Antibaryon shadowing in massive Au + Au collisions at 11 AGeV

Abstract Antibaryon production and the strength of annihilation in baryonic matter is studied for massive reactions ( Au + Au ) at the AGS using the microscopic multiple collision approach RQMD.