Search

Abstract: The hadronization of an expanding partonic fireball is studied within the Parton-Hadron-String Dynamics (PHSD) approach which is based on a dynamical quasiparticle model (DQPM) matched to reproduce lattice QCD results in thermodynamic equilibrium. Apart from strong parton interactions the expansion and development of collective flow is found to be driven by strong gradients in the parton mean-fields. An analysis of the elliptic flow demonstrates a linear correlation with the spatial eccentricity as in the case of ideal hydrodynamics. The hadronization occurs by quark–antiquark fusion or 3 quark/3 antiquark recombination which is described by covariant transition rates. Since the dynamical quarks become very massive, the formed resonant ‘pre-hadronic’ color-dipole states ( or ) are of high invariant mass, too, and sequentially decay to the groundstate meson and baryon octets increasing the total entropy. This solves the entropy problem in hadronization in a natural way. Hadronic particle ratios turn out to be in line with those from a grand-canonical partition function at temperature MeV. [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]