Browsing by Author "Cleymans, J"

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    Centrality dependence of thermal parameters deduced from hadron multiplicities in Au+Au collisions at √sN N = 130 GeV
    (2005) Cleymans, J; Kampfer, B; Kaneta, M; Wheaton, S; Xu, N
    We analyze the centrality dependence of thermal parameters deduced from hadron multiplicities in Au+Au collisions at √sNN = 130 GeV. Although the chemical freeze-out temperature and chemical potentials are found to be roughly centrality independent, the strangeness saturation factor γS increases with participant number toward unity, supporting the assumption of equilibrium freeze-out conditions in central collisions
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    On the chemical equilibration of strangeness-exchange reactions in heavy-ion collisions
    (2005) Cleymans, J; Forster, A; Oeschler, H; Redlich, K; Uhlig, F
    The strangeness-exchange reaction π + Y ↔ K− + N is shown to be the dynamical origin of chemical saturation and equilibration for K− production in heavy-ion collisions up to beam energies of 10 AGeV. The hyperons occurring in this process are produced in association with K+ in baryon–baryon and meson–baryon interactions. This connection is demonstrated by the ratio of K−/K+ which does not vary with centrality and shows a linear correlation with the yield of pions per participant. At incident energies above AGS this correlation no longer holds due to the change in the production mechanism of kaons.
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    Probability distributions in statistical ensembles with conserved charges
    (2005) Cleymans, J; Redlich, K; Turko, L
    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.
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    Towards strangeness saturation in central heavy-ion collisions at high energies
    (Elsevier, 2003) Cleymans, J; Kämpfer, B; Wheaton, S
    It is now well established that particle abundances can be described by statistical-thermal models. In such a way, a large number of observables can be reproduced with a small number of parameters, namely the temperature, baryo-chemical potential and a factor measuring the degree of strangeness saturation. Here we focus on the centrality dependence of the hadron multiplicities and adjust the thermal parameters so as to reproduce the experimental data.
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    Transition from baryonic to mesonic freeze-out
    (2005) Cleymans, J; Oeschler, H; Redlich, K; Wheaton, S
    The recently discovered sharp peak in the K+/π+ ratio in relativistic heavy-ion collisions is discussed in the framework of the statistical model. In this model a rapid change is expected as the hadronic gas undergoes a transition from a baryon-dominated to a meson-dominated gas. The transition occurs at a temperature T=140MeV and baryon chemical potential μB=410MeV corresponding to an incident energy of sNN=8.2GeV. The maximum in the Λ/π ratio is well reproduced by the statistical model, but the change in the K+/π+ ratio is much less pronounced than the one observed by the NA49 Collaboration. The calculated smooth increase of the K−/π− ratio and the shape of the Ξ−/π+ and Ω−/π+ ratios exhibiting maxima at different incident energies is consistent with the presently available experimental data. We conclude that the measured particle ratios with 20–30% deviations agree with a hadronic freeze-out scenario. These deviations seem to occur just in the transition from baryon-dominated to meson-dominated freeze-out.