arXiv subjects
Publications and source records attributed to J. Cleymans.
The rapidity dependence of the chemical freeze-out thermal parameters $T$ and $μ_B$ are determined at the highest RHIC and SPS energies. These show a systematic behavior towards an increase in $μ_B$ away from mid-rapidity and a corresponding decrease in the temperature $T$.
In relativistic nucleus-nucleus collisions the transverse energy per charged particle, E_T/N_ch, increases rapidly with beam energy and remains approximately constant at about 800 MeV for beam energies from SPS to RHIC. It is shown that the hadron resonance gas model describes the energy dependence, as well as the lack of centrality dependence, qualitatively. The values of E_T/N_ch are related to the chemical freeze-out criterium E/N about 1 GeV valid for primordial hadrons.
The system-size dependence of particle production in heavy-ion collisions at the top SPS energy is analyzed in terms of the statistical model. A systematic comparison is made of two suppression mechanisms that quantify strange particle yields in ultra-relativistic heavy-ion collisions: the canonical model with strangeness correlation radius determined from the data and the model formulated in the canonical ensemble using chemical off-equilibrium strangeness suppression factor. The system-size dependence of the correlation radius and the thermal parameters are obtained for p-p, C-C, Si-Si and Pb-Pb collisions at sqrt(s_NN) = 17.3 AGeV. It is shown that on the basis of a consistent set of data there is no clear difference between the two suppression patterns. In the present study the strangeness correlation radius was found to exhibit a rather weak dependence on the system size.
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb collisions at LHC. Hadronic emission in the low-mass region is calculated using in-medium spectral functions of light vector mesons within hadronic many-body theory. In the intermediate-mass region thermal radiation from the Quark-Gluon Plasma, evaluated perturbatively with hard-thermal loop corrections, takes over. An important source over the entire mass range are decays of correlated open-charm hadrons, rendering the nuclear modification of charm and bottom spectra a critical ingredient.
The recently discovered sharp peak in the excitation function of the K+/pi+ ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model, the freeze-out of an ideal hadron gas changes from a situation where baryons dominate to one with mainly mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The calculated maximum in the K+/pi+ ratio is, however, much less pronounced than the one observed by the NA49 Collaboration. The smooth increase of the K-/pi- ratio with incident energy and the shape of the excitation functions of the Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different incident energies, is consistent with the presently available experimental data. The measured K+/pi+ ratio exceeds the calculated one just at the incident energy when the freeze-out condition is changing. We speculate that at this point freeze-out might occur in a modified way. We discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio while most other particle ratios remain essentially unchanged. Such an early freeze-out is supported by results from HBT studies.
Particle yields in heavy ion collisions show an overwhelming evidence for chemical or relative chemical equilibrium at all beam energies. The rapidity dependence of the thermal parameters $T$ and $μ_B$ can now be determined over a wide range of rapidities and show a systematic behavior towards an increase in $μ_B$ away from mid-rapidity.
The systematics of Statistical Model parameters extracted from heavy-ion collisions at lower energies are exploited to extrapolate in the LHC regime. Predictions of various particle ratios are presented and particle production in central Pb-Pb collisions at LHC is discussed in the context of the Statistical Model. The sensitivity of several ratios on the temperature and the baryon chemical potential is studied in detail, and some of them, which are particularly appropriate to determine the chemical freeze-out point experimentally, are indicated. The impact of feed-down contributions from resonances, especially to light hadrons, is illustrated.
The status of the energy dependence of the chemical freeze-out temperature and chemical potential obtained in heavy ion collisions is presented. Recent proposals for chemical freeze-out conditions are compared.
Particle production in central Pb-Pb collisions at LHC is discussed in the context of the Statistical Model. Predictions of various particle ratios are presented with the corresponding choice of model parameters made according to the systematics extracted from heavy-ion collisions at lower energies. The sensitivity of several ratios on the temperature and the baryon chemical potential is studied in detail, and some of them, which are particularly appropriate to determine the chemical freeze-out point experimentally, are indicated. We show that the anti-p / p ratio is most suitable to determine the baryon chemical potential while the Omega / K and Omega / pi ratios are best to determine the temperature at chemical freeze-out.
One of the most remarkable results to emerge from heavy-ion collisions over the past two decades is the striking regularity shown by particle yields at all energies. This has led to several very successful proposals describing particle yields over a very wide range of beam energies, reaching from 1 A GeV up to 200 A GeV, using only one or two parameters. A systematic comparison of these proposals is presented here. The conditions of fixed energy per particle, baryon+anti-baryon density, normalized entropy density as well as percolation model are investigated. The results are compared with the most recent chemical freeze-out parameters obtained in the thermal-statistical analysis of particle yields. The sensitivity and dependence of the results on parameters is analyzed and discussed. It is shown that in the energy range above the top AGS energy, within present accuracies, all chemical freeze-out criteria give a fairly good description of the particle yields. However, the low energy heavy-ion data favor the constant energy per particle as a unified condition of chemical particle freeze-out. This condition also shows the weakest sensitivity on model assumptions and parameters.
The present status of the thermal model is reviewed and the recently discovered sharp peak in the $K^+/π^+$ ratio is discussed in this framework. It is shown that the rapid change is related to a transition from a baryon dominated hadronic gas to a meson dominated one. Further experimental tests to clarify the nature of the transition are discussed. In the thermal model the corresponding maxima in the Xi/pi and Omega/pi ratios occur at slightly different beam energies.
The properties of statistical ensembles with abelian charges close to the thermodynamic limit are discussed. The finite volume corrections to the probability distributions and particle density moments are calculated. Results are obtained for statistical ensembles with both exact and average charge conservation. A new class of variables (semi--intensive variables) which differ in the thermodynamic limit depending on how charge conservation is implemented in the system is introduced. The thermodynamic limit behavior of these variables is calculated through the next to leading order finite volume corrections to the corresponding probability density distributions.
Multiplicities in e+e- annihilation and relativistic heavy ion collisions show remarkable similarities at high energies. A thermal-statistical model is proposed to explain the differences which occur mainly at low beam energies. Two different calculations are performed, one using an approximate thermodynamic relationship, the other using a full thermal model code. The results are in qualitative agreement, suggesting that the interplay of baryon density and temperature tends to systematically suppress the total multiplicity at lower beam energies.
The recently discovered sharp peak in the K+/pi+ ratio in relativistic heavy-ion collisions is discussed in the framework of the thermal 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 = 140 MeV and baryon chemical potential muB = 410 MeV corresponding to an incident energy of 8.2 GeV.
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.
The recently discovered sharp peak in the K+/pi+ ratio 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 happens at sqrt{s_{NN}} = 8.16 GeV, temperature T = 140 MeV and baryon chemical potential mu_B = 410 MeV. The maximum in the Lambda/pi ratio is well reproduced by the statistical model, but the change in the K+/pi+ ratio is much less pronounced than the one observed by the NA49 collaboration. Further experimental tests are proposed to clarify the nature of the transition. In particular, the maxima expected in the statistical model for the Xi/pi and Omega/pi ratios occur at slightly higher beam energies than the maxima for the Lambda/pi and K+/pi+ ratios.
Selected results obtained using THERMUS, a newly-developed statistical-thermal model analysis package, are presented.
We analyse the centrality dependence of thermal parameters deduced from hadron m ultiplicities in Au + Au collisions at $\sqrt{s_{NN}} = 130 GeV$. While the chemical freeze-out temperature and chemical potentials are found to be roughly centrality-independent, the strangeness saturation factor $γ_S$ increases with participant number towards unity, supporting the assumption of equilibrium freeze-out conditions in central collisions.