A novel scenario for the production of antihyperons in relativistic heavy ion collisions

We elaborate on our recent suggestion on antihyperon production in relativistic heavy ion collisions by means of multi-mesonic (fusion-type) reactions. It will be shown that the (rare) antihyperons are driven towards chemical equilibrium with pions, nucleons and kaons on a timescale of 1--3 fm/c in a still moderately baryon-dense hadronic environment.Comment: 4 pages, 3 figures, Contr. to QM2001: 15th. International Conference on Ultra-Relativistic Nucleus-Nucleus Collision

Importance of multi-mesonic fusion processes on (strange) antibaryon production

Sufficiently fast chemical equilibration of (strange) antibaryons in an environment of nucleons, pions and kaons during the course of a relativistic heavy ion collision can be understood by a `clustering' of mesons to build up baryon-antibaryon pairs. This multi-mesonic (fusion-type) process has to exist in medium due to the principle of detailed balance. Novel numerical calculations for a dynamical setup are presented. They show that - at maximum SPS energies - yields of each antihyperon specie are obtained which are consistent with chemical saturated populations of T approximately 150-160 MeV, in line with popular chemical freeze-out parameters extracted from thermal model analyses.Comment: 14 pages, 8 figures; new version in standard reftex; version of proceedings attached as postscript file; invited talk at CRIS2002, 4th Catania Relativistic Ion Studies, Exotic Clustering, June 10-14, 200

Chemical Equilibration of Antihyperons

Rapid chemical equilibration of antihyperons by means of the interplay between strong annihilation on baryons and the corresponding backreactions of multi-mesonic (fusion-type) processes in the later, hadronic stage of an ultrarelativistic heavy ion collision will be discussed. Explicit rate calculations for a dynamical setup are presented. At maximum SPS energies yields of each antihyperon specie are obtained which are consistent with chemical saturated populations of $T \approx 150-160$ MeV. The proposed picture supports dynamically the popular chemical freeze-out parameters extracted within thermal models.Comment: revised version for some typos and two references; 6 pages, 4 figures; contribution to the Int. Workshop XXX on Gross Properties of Nuclei and Nuclear Excitations: Ultrarelativistic Heavy-Ion Collisions, Hirschegg, Jan. 13 - 19, 200

Review of the "Bottom-Up" scenario

Thermalization of a longitudinally expanding color glass condensate with Bjorken boost invariant geometry is investigated within parton cascade BAMPS. Our main focus lies on the detailed comparison of thermalization, observed in BAMPS with that suggested in the Bottom-Up scenario. We demonstrate that the tremendous production of soft gluons via $gg \to ggg$, which is shown in the Bottom-Up picture as the dominant process during the early preequilibration, will not occur in heavy ion collisions at RHIC and LHC energies, because the back reaction $ggg\to gg$ hinders the absolute particle multiplication. Moreover, contrary to the Bottom-Up scenario, soft and hard gluons thermalize at the same time. The time scale of thermal equilibration in BAMPS calculations is of order \as^{-2} (\ln \as)^{-2} Q_s^{-1}. After this time the gluon system exhibits nearly hydrodynamic behavior. The shear viscosity to entropy density ratio has a weak dependence on $Q_s$ and lies close to the lower bound of the AdS/CFT conjecture.Comment: Quark Matter 2008 Proceeding

Statistical description with anisotropic momentum distributions for hadron production in nucleus-nucleus collisions

The various experimental data at AGS, SPS and RHIC energies on hadron particle yields for central heavy ion collisions are investigated by employing a generalized statistical density operator, that allows for a well-defined anisotropic local momentum distribution for each particle species, specified by a common streaming velocity parameter. The individual particle ratios are rather insensitive to a change in this new intensive parameter. This leads to the conclusion that the reproduction of particle ratios by a statistical treatment does not imply the existence of a fully isotropic local momentum distribution at hadrochemical freeze-out, i.e. a state of almost complete thermal equilibrium.Comment: 14 pages, revtex, 3 figures accepted version, to be published in Journal of Physics