Chemical Freeze-out Parameters Research Articles

Particle Ratios at CERN, BNL and GSI : Unified description of Freeze-Out Parameters

It is shown that the chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV for the average energy per hadron.

Chemical and thermal freeze-out parameters from1Ato200AGeV

The present knowledge about hadrons produced in relativistic heavy ion collisions is compatible with chemical freeze-out happening when the energy density divided by the particle density reaches the value of 1 GeV. This observation is used to determine the energy dependence of the chemical freeze-out parameters T_{ch} and mu_B^{ch} for beam energies varying between 1 and 200 A.GeV. The consequences of this energy dependence are studied for various particle ratios. Predictions for particle ratios at beam energy 40 A.GeV are presented. The conditions for thermal freeze-out are also determined. These correspond either to an energy density of 45 MeV/fm**3 or to a particle density of 0.05/fm**3.

Chemical nonequilibrium and deconfinement in 200AGeV sulphur induced reactions

We interpret hadronic particle abundances produced in S--Au/W/Pb 200 A GeV reactions in terms of the final state hadronic phase space model and determine by a data fit of the chemical hadron freeze-out parameters. Allowing for the flavor abundance non-equilibrium a highly significant fit to experimental particle abundance data emerges, which supports possibility of strangeness distillation. We find under different strategies stable values for freeze-out temperature T_f=143\pm3 MeV, baryochemical potential \mu_B= 173\pm6 MeV, ratio of strangeness (\gamma_s) and light quark (\gamma_q) phase space occupancies \gamma_s/\gamma_q=0.60\pm0.02, and \gamma_q=1.22\pm0.05 without accounting for collective expansion (radial flow). When introducing flow effects which allow a consistent description of the transverse mass particle spectra, yielding |v_c|=0.49\pm0.01c, we find \gamma_s/\gamma_q=0.69\pm0.03, \gamma_q=1.41\pm0.08. The strange quark fugacity is fitted at \lambda_s=1.00\pm0.02 suggesting chemical freeze-out directly from the deconfined phase.

Particle ratios at SPS, AGS and SIS

Ratios of integrated particle yields provide the best method for determining the temperature and chemical potential. The chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS and GSI/SIS energies all correspond to a unique value of 1 GeV per hadron in the local rest frame of the system, independent of the beam energy and of the target and beam particles.

Unified Description of Freeze-Out Parameters in Relativistic Heavy Ion Collisions

It is shown that the chemical freeze-out parameters obtained at CERN/SPS, BNL/AGS, and GSI/SIS energies all correspond to a unique value of 1 GeV for the average energy per hadron in the local rest frame of the system, independent of the beam energy and of the target and beam particles.

Chemical freeze-out conditions in central S-S collisions at 200A GeV

We determine the chemical freeze-out parameters of hadronic matter formed in central S-S collisions at 200 A GeV, analyzing data from the NA35 collaboration at CERN. In particular we study the quark (baryon number) and strange quark fugacities, as well as the strange quark phase-space occupancy and the freeze-out temperature. The strange quark chemical potential is found to be consistent with zero, and the strange quark abundance is found to be saturated as would be expected for the deconfined phase. We study the stability of our results against variations in the analysis procedure and with respect to a restriction of the data to the central rapidity region. The same analysis applied to nucleonnucleon data yields significantly different freeze-out parameters, in particular regarding the degree of strangeness saturation.