We present a calculation of e + e − production in γA reactions at MAMI and TJNAF energies within a semi-classical BUU transport model. Dilepton invariant mass spectra for γC, γCa and γPb are calculated at 0.8, 1.5 and 2.2 GeV. We focus on observable effects of medium modifications of the ρ and ω

We analyse the production and propagation of pions and kaons in heavy-ion reactions from 0.8 -1.8 A·GeV within a coupled channel transport approach including the kaon production channelsAssuming the hyperon selfenergy to be 2/3 of the nucleon selfenergy we find that all inclusive experimental K + spectra at SIS energies can be reproduced reasonably well without any selfenergies for the kaons although a slightly repulsive kaon potential cannot be excluded by the present data on kaon spectra and flow. : 25.75.+r, 13.75 y PACS

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We present a dynamical study of e + e − production in C + C and Ca + Ca collisions at BEVALAC/SIS energies on the basis of the covariant transport approach HSD employing momentum-dependent ρ-meson spectral functions that include the pion modifications in the nuclear medium as well as the polarization of the ρ-meson due to resonant ρ−N scattering. We find that the experimental data from the DLS collaboration cannot be described within the ρ-meson spectral function approach. A dropping η-mass scenario leads to a good reproduction of the DLS dilepton data, however, violates the m Tscaling of π 0 and η spectra as observed by the TAPS collaboration as well as η photoproduction on nuclei. PACS

We review the collectivity and the suppression pattern of charmed mesons -produced in proton-nucleus and nucleus-nucleus collisions at SPS (∼ 158 A·GeV) and RHIC energies (∼ 21 A·TeV) -in comparison to dynamical and thermal models. In particular, we examine the charmonium 'melting' and the 'comover dissociation' scenarios -implemented in a microscopic transport approach -in comparison to the available data from the SPS and RHIC. The analysis shows that the dynamics of c,c quarks at RHIC are dominated by partonic or 'pre-hadronic' interactions in the strongly coupled plasma stage and can neither be modeled by 'hadronic' interactions nor described appropriately by color screening alone. Both the 'charmonium melting' and the hadronic 'comover absorption and recreation model' are found, however, to be compatible with the experimental observation at SPS energies; the experimental ratio of Ψ ′ /J/Ψ versus centrality clearly favors the 'hadronic comover' scenario. We find that the collective flow of charm in the purely hadronic Hadron-String Dynamics (HSD) transport appears compatible with the data at SPS energies, but substantially underestimates the data at top RHIC energies. Thus, the large elliptic flow v 2 of D-mesons and the low R AA (p T ) of J/Ψ seen experimentally have to be attributed to early interactions of non-hadronic degrees of freedom. Simultaneously, we observe that non-hadronic interactions are mandatory in order to describe the narrowing of the J/Ψ rapidity distribution from pp to central Au + Au collisions at the top RHIC energy of √ s = 200 GeV. We demonstrate additionally that the strong quenching of high-p T J/Ψ's in central Au + Au collisions indicates that a large fraction of final J/Ψ mesons is created by a coalescence mechanism close to the phase boundary. Throughout this review we, furthermore, provide predictions for charm observables from Au+Au collisions at FAIR energies of 25 -35 A·GeV.