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 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.

We calculate the cross sections for inclusive one-pion, two-pion and eta photoproduction in nuclei in the photon energy range from 300 MeV to 900 MeV within the framework of a semi-classical BUU transport model. Our results are compared with existing experimental data and discussed with respect to a calculation of the total photoabsorption cross section.Comment: 30 pages LaTeX including 13 postscript figure

We calculate the baryon flow P x /A(y) in the energy range from .25 to ≤2.5AGeV in a relativistic transport model for N i + N i and Au + Au collisions employing various models for the baryon self energies. We find that to describe the flow data of the FOPI Collaboration the strength of the vector potential has to be reduced at high relative momentum or at high density such that the Schrödinger-equivalent potential at normal nuclear density decreases above 1GeV relative kinetic energy and approaches zero above 2GeV .