Comparison of chemical freeze-out criteria in heavy-ion collisions

Abstract

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 1A GeV up to 200A 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 energy of the BNL Alternating Gradient Synchrotron 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.

Melting hadrons, boiling quarks

“…The SHARE LHC freeze-out temperature is clearly below the lattice critical temperature range. The results of other groups are obtained with simplified parameter sets: marked GSI [80,81], Florence [82][83][84], THERMUS [85], STAR [86] and AL-ICE [87,88]. These results show the chemical freeze-out temperature T in general well above the lattice T H .…”

“…This complete set is necessary since the observed particle set includes particles arising from [71,72], the SHM-SHARE results (full circles) [7,[73][74][75][76][77][78][79] and results of other groups [80][81][82][83][84][85][86][87][88]. Figure from ref.…”

Statistical ensembles with finite bath: A description for an event generator

“…One notes that the scaled variances and correlation coefficients in the respective acceptance bins in Figs. 11 and 12 are generally larger than the acceptance scaling procedure 7 suggests, with the notable exception of ρ +− ( p T ,5 ).…”

“…If one would construct now a larger and larger number of momentum-space bins of equal average particle multiplicities, 7 For the acceptance scaling approximation it is assumed that particles are randomly detected with a certain probability q = 0.2, independent of their momentum. one would successively lose more and more information about how multiplicities of distinct groups of particles are correlated.…”

“…Over time this has led to the establishment of the "chemical freeze-out line" [7], which is now a vital part of our understanding of the phase diagram of strongly interacting matter. Model predictions for the upcoming LHC and future FAIR [8,9] experiments largely follow these trends.…”