The Statistical Model of Hadrogenesis in A--A collisions from AGS to SPS and RHIC

We discuss experimental data on particle yields and particle spectra obtained in heavy ion collisions in a very broad energy range from SIS/GSI through AGS/BNL up to SPS/CERN and RHIC/BNL. We argue that in this broad energy range hadronic yields and their ratios resemble a thermal equilibrium population along a unified freeze--out curve determined by the condition of fixed energy/particle = 1 GeV. At RHIC and top SPS, thermal parameters are consistent within error with the critical conditions required for deconfinement. This, together with the particular distribution of strangeness within a collision fireball, could indicate that chemical equilibrium is a direct consequence of parton to hadron transition, which populates a state of maximum entropy. At lower energies equilibration in A--A collisions should appear through hadronic interactions and rescatterings.Comment: Plenary talk given at: International Nuclear Physics Conference, INPC2001, Berkeley, USA, August 200

Strangeness enhancement and Energy dependence in Heavy Ion Collisions

The canonical statistical model analysis of strange and multistrange hadron production in central A-A relative to p-p/p-A collisions is presented over the energy range from $\sqrt s=8.73$ GeV up to $\sqrt s =130$ GeV. It is shown that the relative enhancement of strange particle yields from p-p/p-A to A-A collisions substantially increases with decreasing collision energy. It is largest at $\sqrt s= 8.7$ GeV, where the enhancement of $\Omega,\Xi$ and $\Lambda$ is of the order of 100, 20 and 3, respectively. In terms of the model these results are due to the canonical suppression of particle thermal phase space at lower energies, which increases with the strangeness content of the particle and with decreasing size of the collision fireball. The comparison of the model with existing data on energy dependence of the kaon/pion ratio is also discussed

Probability distributions in statistical ensembles with conserved charges

The probability distributions for charged particle numbers and their densities are derived in statistical ensembles with conservation laws. It is shown that if this limit is properly taken then the canonical and grand canonical ensembles are equivalent. This equivalence is proven on the most general, probability distribution level.Comment: 5 pages. A little bit shorter version due to some editorial and language changes. To be published in Phys. Rev.

Charmonium Production from the Secondary Collisions at LHC Energy

We consider the charmonium production in thermalized hadronic medium created in ultrarelativistic heavy ion collisions at LHC energy. The calculations for the secondary $J/\psi$ and $\psi^,$ production by $D\bar D$ annihilation are performed within a kinetic model taking into account the space-time evolution of a longitudinally and transversely expanding medium. We show that the secondary charmonium production appears almost entirely during the mixed phase and it is very sensitive to the charmonium dissociation cross section with co-moving hadrons. Within the most likely scenario for the dissociation cross section of the $J/\psi$ mesons their regeneration in the hadronic medium will be negligible. The secondary production of $\psi^,$ mesons however, due to their large cross section above the threshold, can substantially exceed the primary yield.Comment: ps file 11

The canonical effect in statistical models for relativistic heavy ion collisions

Enforcing exact conservation laws instead of average ones in statistical thermal models for relativistic heavy ion reactions gives raise to so called canonical effect, which can be used to explain some enhancement effects when going from elementary (e.g. pp) or small (pA) systems towards large AA systems. We review the recently developed method for computation of canonical statistical thermodynamics, and give an insight when this is needed in analysis of experimental data.Comment: 4 pages, 3 figures. Talk given in Strangeness in Quark Matter, Frankfurt am Main 2001. Submitted to J. Phys. G: Nucl. Part. Phy

Kurtosis and compressibility near the chiral phase transition

The properties of net quark number fluctuations in the vicinity of the QCD chiral phase transition are discussed in terms of an effective chiral model in the mean-field approximation. We focus on the ratio of the fourth- to second- order cumulants (kurtosis) and the compressibility of the system and discuss their dependence on the pion mass. It is shown that near the chiral phase transition, both observables are sensitive to the value of $m_\pi$. For physical $m_\pi$, the kurtosis exhibits a peak whereas the inverse compressibility shows a dip at the pseudocritical temperature. These structures disappear for large $m_\pi$. Our results, obtained in an effective model with two flavors, are qualitatively consistent with recent results of 2+1 flavor lattice gauge theory. We also discuss the high- and low-temperature properties of these observables and the role of the coupling of the quark degrees of freedom to the Polyakov loop

Susceptibilities and the Phase Structure of a Chiral Model with Polyakov Loops

In an extension of the Nambu-Jona-Lasinio model where the quarks interact with the temporal gluon field, represented by the Polyakov loop, we explore the relation between the deconfinement and chiral phase transitions. The effect of Polyakov loop dynamics on thermodynamic quantities, on the phase structure at finite temperature and baryon density and on various susceptibilities is presented. Particular emphasis is put on the behavior and properties of the fluctuations of the (approximate) order parameters and their dependence on temperature and net--quark number density. We also discuss how the phase structure of the model is influenced by the coupling of the quarks to the Polyakov loop.Comment: 18 pages, 22 figures; text rearranged and references added. results and conclusions unchanged; final version accepted for publication in Phys. Rev.