828 research outputs found

    Density Perturbations in Heavy-Ion Collisions below the Critical Point

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    Heavy ion collisions at large baryon density may exhibit a first order phase transition from a chirally symmetric phase to the symmetry broken ground state. This should then lead to large density inhomogeneities, which affect the relative hadron multiplicities.Comment: 1 page, 1 figure, contribution to the GSI annual report 200

    Hadron yields from thermalized minijets at RHIC and LHC

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    We calculate the yields of pions, kaons, and ϕ\phi-mesons for RHIC and LHC energies assuming thermodynamical equilibration of the produced minijets, and using as input results from pQCD for the energy densities at midrapidity. In the calculation of the production of partons and of transverse energy one has to account for nuclear shadowing. By using two parametrizations for the gluon shadowing one derives energy densities differing strongly in magnitude. In this publication we link those perturbatively calculated energy densities of partons via entropy conservation in an ideal fluid to the hadron multiplicities at chemical freeze-out.Comment: Talk given at the International Europhysics Conference on High Energy Physics, EPS-HEP99, Tampere, Finland, July 1999, 3 page

    In-medium vector meson masses in a Chiral SU(3) model

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    A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the effects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation effects from the nucleon sector and is not observed in the mean field approximation.Comment: 26 pages including 10 figures; the text has been modified for clarit

    Transport calculation of dilepton production at ultrarelativistic energies

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    Dilepton spectra are calculated within the microscopic transport model UrQMD and compared to data from the CERES experiment. The invariant mass spectra in the region 300 MeV < M < 600 MeV depend strongly on the mass dependence of the ρ\rho meson decay width which is not sufficiently determined by the Vector Meson Dominance model. A consistent explanation of both the recent Pb+Au data and the proton induced data can be given without additional medium effects

    Entropy Production in Collisions of Relativistic Heavy Ions -- a signal for Quark-Gluon Plasma phase transition?

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    Entropy production in the compression stage of heavy ion collisions is discussed within three distinct macroscopic models (i.e. generalized RHTA, geometrical overlap model and three-fluid hydrodynamics). We find that within these models \sim 80% or more of the experimentally observed final-state entropy is created in the early stage. It is thus likely followed by a nearly isentropic expansion. We employ an equation of state with a first-order phase transition. For low net baryon density, the entropy density exhibits a jump at the phase boundary. However, the excitation function of the specific entropy per net baryon, S/A, does not reflect this jump. This is due to the fact that for final states (of the compression) in the mixed phase, the baryon density \rho_B increases with \sqrt{s}, but not the temperature T. Calculations within the three-fluid model show that a large fraction of the entropy is produced by nuclear shockwaves in the projectile and target. With increasing beam energy, this fraction of S/A decreases. At \sqrt{s}=20 AGeV it is on the order of the entropy of the newly produced particles around midrapidity. Hadron ratios are calculated for the entropy values produced initially at beam energies from 2 to 200 AGeV.Comment: 17 pages, 8 figures, uses epsfig.sty; Submitted to Nucl.Phys.

    Hypernuclei, dibaryon and antinuclei production in high energy heavy ion collisions: Thermal production vs. Coalescence

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    We study the production of (hyper-)nuclei and di-baryons in most central heavy Ion collisions at energies of Elab=1−160AE_{lab}=1-160 A GeV. In particular we are interested in clusters produced from the hot and dense fireball. The formation rate of strange and non-strange clusters is estimated by assuming thermal production from the intermediate phase of the UrQMD-hydro hybrid model and alternatively by the coalescence mechanism from a hadronic cascade model. Both model types are compared in detail. For most energies we find that both approaches agree in their predictions for the yields of the clusters. Only for very low beam energies, and for di-baryons including Ξ\Xi's, we observe considerable differences. We also study the production of anti-matter clusters up to top RHIC energies and show that the observation of anti-4He^4He and even anti-Λ4He^4_{\Lambda}He is feasible. We have found a considerable qualitative difference in the energy dependence of the strangeness population factor RHR_H when comparing the thermal production with the coalescence results.Comment: 9 pages, 8 figures and 2 tables, version accepted by PL

    Open-charm enhancement at FAIR?

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    We have calculated the D-meson spectral density at finite temperature within a self-consistent coupled-channel approach that generates dynamically the Λc\Lambda_c (2593) resonance. We find a small mass shift for the D-meson in this hot and dense medium while the spectral density develops a sizeable width. The reduced attraction felt by the D-meson in hot and dense matter together with the large width observed have important consequences for the D-meson production in the future CBM experiment at FAIR.Comment: 4 pages, 2 figures, to appear in the proceedings of 9th International Conference on Strangeness in Quark Matter (SQM2006), Los Angeles, USA, March 26-31, 200
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