We analyze the experimental hadron yield ratios for central nucleus-nucleus collisions in terms of thermal model calculations over a broad energy range, √ s N N =2.7-200 GeV. The fits of the experimental data with the model calculations provide the thermal parameters, temperature and baryo-chemical potential at chemical freezeout. We compare our results with the values obtained in other studies and also investigate more technical aspects such as a potential bias in the fits when fitting particle ratios or yields. Using parametrizations of the temperature and baryonic chemical potential as a function of energy, we compare the model calculations with data for a large variety of hadron yield ratios. We provide quantitative predictions for experiments at LHC energy, as well as for the low RHIC energy of 62.4 GeV. The relation of the determined parameters with the QCD phase boundary is discussed.

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We present an analysis of particle production yields measured in central Au-Au collisions at RHIC in the framework of the statistical thermal model. We demonstrate that the model extrapolated from previous analyses at SPS and AGS energy is in good agreement with the available experimental data at √ s = 130 GeV implying a high degree of chemical equilibration. Performing a χ 2 fit to the data, the range of thermal parameters at chemical freezeout is determined. At present, the best agreement of the model and the data is obtained with the baryon chemical potential µ B ≃ 46 ± 5 MeV and temperature T ≃ 174 ± 7 MeV. More ratios, such as multistrange baryon to meson, would be required to further constrain the chemical freezeout conditions. Extrapolating thermal parameters to higher energy, the predictions of the model for particle production in Au-Au reactions at √ s = 200GeV are also given.

Recent studies based on lattice Monte Carlo simulations of quantum chromodynamics (QCD)-the theory of strong interactions-have demonstrated that at high temperature there is a phase change from confined hadronic matter to a deconfined quark-gluon plasma in which quarks and gluons can travel distances that greatly exceed the size of hadrons. Here we show that the phase structure of such strongly interacting matter can be decoded by analysing particle production in high-energy nuclear collisions within the framework of statistical hadronization, which accounts for the thermal distribution of particle species. Our results represent a phenomenological determination of the location of the phase boundary of strongly interacting matter, and imply quark-hadron duality at this boundary.

To investigate a recent proposal that J/ψ production in ultra-relativistic nuclear collisions is of thermal origin we have reanalyzed the data from the NA38/50 collaboration within a thermal model including charm. Comparison of the calculated with measured yields demonstrates the non-thermal origin of hidden charm production at SPS energy. However, the ratio ψ ′ /(J/ψ) exhibits, in central nucleus-nucleus collisions, thermal features which lead us to a new interpretation of open charm and charmonium production at SPS energy. Implications for RHIC and LHC energy measurements will be discussed.The suppression of J/ψ mesons (compared to what is expected from hard scattering models) was early on predicted [1] to be a signature for color deconfinement. Data for Sinduced collisions exhibited a significant suppression but systematic studies soon revealed that such suppression exists already in p-nucleus collisions and is due to the absorption in (normal) nuclear matter of a pre-resonant state consisting, e.g., of a color singlet ccg state that is formed on the way towards J/ψ production. The situation has been summarized in [2][3][4].The newest data for Pb+Pb collisions now exhibit clear evidence for anomalous absorption beyond the standard nuclear absorption expected for such systems. The most recent results are summarized in [5][6][7]. The observed anomalous suppression is not explained in conventional models where the charmonia are broken up by interactions with co-movers as discussed in [5]. For a discussion of the present status of J/ψ suppression and its understanding in terms of phenomenological models see [8].However, it was recently conjectured [9,10] that J/ψ production is of thermal origin and exhibits no direct connection to color deconfinement. Since the charmonia are heavy mesons with masses much larger than any conceivable temperature, thermal production would be a big surprize. On the other hand, substantial evidence now exists [11][12][13][14][15][16][17] that hadron production (other than charmonia) in ultra-relativistic nuclear collisions proceeds through a state of chemical equilibrium near or at the phase boundary between hadron

An improved statistical model with excluded volume corrections and resonance decays is introduced and applied to the complete presently available set of particle ratios as measured by the various experiments at the SPS in Pb+Pb collisions. The results imply that a high degree of hadrochemical equilibration is reached at chemical freeze-out in Pb+Pb collisions.

The rather complete data set of hadron yields from central Si + A collisions at the Brookhaven AGS is used to test whether the system at freeze-out is in thermal and hadro-chemical equilibrium. Rapidity and transverse momentum distributions are discussed with regards to the information they provide on hydrodynamic flow.The goal of the ultra-relativistic heavy-ion program at the BNL AGS and CERN SPS is to study highly excited and dense nuclear matter and possibly the transition from hot and dense hadronic matter to deconfined quark-matter with restored chiral symmetry. While future collider experiments will probe a hot quark-gluon plasma with low net baryon density, present fixed target experiments create matter, possibly quark-matter, at very high baryon density and moderate temperature.The present paper is following up on an earlier suggestion by some of us [1], based on the first AGS and SPS data, that a high degree of thermalization is reached and that there is evidence for hydrodynamic expansion of the created fireball. We now use the much larger set of data from central Si + A collisions at the AGS first to discuss quantitatively the 1