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Abstract: Within a hadron-string dynamical transport approach (HSD) we investigate the attenuation of high transverse momentum () hadrons as well as the suppression of ‘near-side’ and ‘far-side’ jets in Au+Au collisions at invariant energies and in comparison to the data available from the Relativistic Heavy-Ion Collider (RHIC). From our transport studies we find that a significant part of the high hadron attenuation seen experimentally can be attributed to inelastic interactions of ‘leading’ pre-hadrons with the dense hadronic environment. In addition, we also show results of ‘near-side’ and ‘far-side’ angular correlations of high particles from Au+Au collisions at and within this (pre-)hadronic attenuation scenario. It turns out that the ‘near-side’ correlations are unaltered—in accordance with experiment—whereas the ‘far-side’ correlations are suppressed by up to ∼ 60% in central collisions. Since a much larger suppression is observed experimentally for these reactions in central reactions we conclude that there should be strong additional (and earlier) partonic interactions in the dense and possibly colored medium created in Au+Au collisions at RHIC. [Copyright &y& Elsevier]

We investigate hadron formation in deep inelastic lepton scattering on N, Kr and Xe nuclei in the kinematic regime of the HERMES experiment. The elementary electron–nucleon interaction is described within the event generator PYTHIA while a full coupled-channel treatment of the final state interactions is included by means of a BUU transport model. We find a good agreement with the measured charged hadron multiplicity ratio RMh for N and Kr targets by accounting for the deceleration and absorption of the primarily produced particles as well as for the creation of secondary hadrons in the final state interactions. [Copyright &y& Elsevier]

We investigate hadron production and attenuation of hadrons with strange and charm quarks (or antiquarks) as well as high transverse momentum hadrons in relativistic nucleus–nucleus collisions from 2 A GeV to 21.3 A TeV within two independent transport approaches (UrQMD and HSD). Both transport models are based on quark, diquark, string and hadronic degrees of freedom, but do not include any explicit phase transition to a quark–gluon plasma. From our dynamical calculations we find that both models do not describe the maximum in the K+/π+ ratio at 20–30 A GeV in central Au+Au collisions found experimentally, though the excitation functions of strange mesons are reproduced well in HSD and UrQMD. Furthermore, the transport calculations show that the charmonium recreation by D+&Dmacr;→J/Ψ+meson reactions is comparable to the dissociation by ‘comoving’ mesons at RHIC energies contrary to SPS energies. This leads to the final result that the total J/Ψ suppression as a function of centrality at RHIC should be less than the suppression seen at SPS energies where the ‘comover’ dissociation is substantial and the backward channels play no role. Furthermore, our transport calculations—in comparison to experimental data on transverse momentum spectra from pp, d+Au and Au+Au reactions—show that pre-hadronic effects are responsible for both the hardening of the hadron spectra for low transverse momenta (Cronin effect) as well as the suppression of high pT hadrons. The mutual interactions of formed hadrons are found to be negligible in central Au+Au collisions at √ of s=200 GeV for pT≥6 GeV/c and the sizeable suppression seen experimentally is attributed to a large extent to the interactions of ‘leading’ pre-hadrons with the dense environment. [Copyright &y& Elsevier]

Abstract: Charmonium production and suppression in In+In and Pb+Pb reactions at SPS energies is investigated with the HSD transport approach within the ‘hadronic comover model’ as well as the ‘QGP threshold scenario’. The results of the transport calculations for suppression and the to ratio are compared with the recent data of the NA50 and NA60 Collaborations. We find that the comover absorption model—with a single parameter for the matrix element squared for charmonium-meson dissociation—performs best with respect to all data sets. The ‘threshold scenario’—within different assumptions for the melting energy densities—yields a reasonable suppression for but fails in reproducing the to ratio for Pb+Pb at . Predictions for Au+Au reactions are presented for a bombarding energy of in the different scenarios which will allow for a clear distinction between the models from the experimental side at the future FAIR facility. [Copyright &y& Elsevier]