Ch. Hartnack

What determines the K- multiplicity at energies around (1-2)A GeV?

In heavy ion reactions at energies around (1-2)A GeV the measured K- yields appear rather high as compared to pp collisions as shown by the KaoS Collaboration. Employing quantum molecular dy-namics simulations, we show that this is caused by the fact that the dominant production channel is not BB-->BBK+K- but the mesonic Lambda(Sigma)pi-->K-B reaction. Because the Lambda (Sigma) stem from the reaction BB-->Lambda(Sigma)K+B, the K+ and the K- yield are strongly correlated, i.e., the K(-)/K(+) ratio occurs to be nearly independent of the impact parameter as found experimentally. The final K- yield is strongly influenced by the K+N [due to their production via the Lambda(Sigma)] but very little by the K-N potential.

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.

Constraining the nuclear matter equation of state around twice saturation density

Abstract Using FOPI data on elliptic flow in Au + Au collisions between 0.4 and 1.5 A GeV we extract constraints for the equation of state (EOS) of compressed symmetric nuclear matter using the transport code IQMD by introducing an observable describing the evolution of the size of the elliptic flow as a function of rapidity. This observable is sensitive to the nuclear EOS and a robust tool to constrain the compressibility of nuclear matter up to 3 ρ 0 .

Beyond mean field confrontation of different models with high transverse momentum proton spectra

Abstract Several models have been proposed to simulate heavy ion reactions beyond the mean field level. The lack of data in phase space regions which may be sensitive to different treatments of fluctuations made it difficult to judge these approaches. The recently published high energy proton spectra, measured in the reaction 94 AMeV Ar + Ta, allow for the first time for a comparison of the models with data. We find that these spectra are reproduced by Quantum Molecular Dynamics (QMD) calculations. Models in which effective collective effects are introduced lead to too large proton yields. High energy proton production hence does not seem to require collective effects such as the ones needed to understand well below threshold kaon production.

Analysis of kaon spectra at SIS energies—what remains from the KN potential?

We study the reaction Au+Au at 1.48 A GeV and analyse the influence of the KN optical potential on cm spectra and azimuthal distributions at mid-rapidity. We find a significant change of the yields but only slight changes in the shapes of the distributions when turning off the optical potential. However, the spectra show contributions from different reaction times, where early kaons contribute stronger to higher momenta and late kaons to lower momenta. Azimuthal distributions of the kaons at mid-rapidity show a strong centrality dependence. Their shape is influenced by the KN optical potential as well as by rescattering.