We analyse the production and propagation of kaons and antikaons in Ni + Ni reactions from 0.8-1

We investigate the production of pions in heavy-ion collisions in the energy range of 1 -2 GeV/A. The dynamics of the nucleus-nucleus collisions is described by a set of coupled transport equations of the Boltzmann-Uehling-Uhlenbeck type for baryons and mesons. Besides the N (938) and the ∆(1232) we also take into account nucleon resonances up to masses of 1.9 GeV /c 2 as well as π-, η-and ρ-mesons. We study in detail the influence of the higher baryonic resonances and the 2π-production channels (N N → N N ππ) on the pion spectra in comparison to π − data from Ar + KCl collisions at 1.8 GeV/A and π 0 -data for Au + Au at 1.0 GeV/A. We, furthermore, present a detailed comparison of differential pion angular distributions with the BEVALAC data for Ar + KCl at 1.8 GeV/A. The general agreement obtained indicates that the overall reactions dynamics is well described by our novel transport approach.

We calculate the subthreshold production of antiprotons in the Lorentzcovariant RBUU approach employing a weighted testparticle method to treat the antiproton propagation and absorption nonperturbatively. We find that the antiproton differential cross sections are highly sensitive to the baryon and antiproton selfenergies in the dense baryonic environment. Adopting the baryon scalar and vector selfenergies from the empirical optical potential for proton-nucleus elastic scattering and from Dirac-Brueckner calculations at higher density ρ > ρ 0 we examine the differential antiproton spectra as a function of the antiproton selfenergy. A detailed comparison with the available experimental data for p-nucleus and nucleus-nucleus reactions shows that the antiproton feels a moderately attractive mean-field at normal nuclear matter density ρ 0 which is in line with a dispersive potential extracted from the free annihilation cross section. † Supported by BMFT, GSI Darmstadt and KFA Jülich.

We calculate the total photoabsorption cross section on nuclei in the energy range from 300 MeV to 1 GeV within the framework of a semi-classical phase space model. Besides medium modifications like Fermi motion and Pauli blocking we focus on the collision broadening of the involved resonances. The resonance contributions to the elementary cross section are fixed by fits to partial wave amplitudes of pion photoproduction. The cross sections for $N \, R \to N \, N$, needed for the calculation of collision broadening, are obtained by detailed balance from a fit to $N \, N \to N \, N \, \pi$ cross sections. We show that a reasonable collision broadening is not able to explain the experimentally observed disappearance of the $D_{13}(1520)$-resonance in the photoabsorption cross section on nuclei.Comment: 26 pages Latex including 9 postscript figure

We study the dynamics of charged pions in the nuclear medium via the ratio of differential π − -and π + -spectra in a coupled-channel BUU (CBUU) approach. The relative energy shift of the charged pions is found to correlate with the pion freeze-out time in nucleus-nucleus collisions as well as with the impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb force provides a 'clock' for the expansion of the hot nuclear system. Detailed comparisons with experimental data for Au + Au at 1 GeV/A and N i + N i at 2.0 GeV/A are presented.