Jozso's Legacy: Chemical and Kinetic Freeze-out in Heavy-Ion Collisions

Abstract

We review J. Zimanyi's key contributions to the theoretical understanding of dynamical freeze-out in nuclear collisions and their subsequent applications to ultra-relativistic heavy-ion collisions, leading to the discovery of a freeze-out hierarchy where chemical freeze-out of hadron yields precedes the thermal decoupling of their momentum spectra. Following Zimanyi's lines of reasoning we show that kinetic freeze-out necessarily leads to a dependence of the corresponding freeze-out temperature on collision centrality. This centrality dependence can be predicted within hydrodynamic models, and for Au+Au collisions at RHIC this prediction is shown to reproduce the experimentally observed centrality dependence of the thermal decoupling temperature, extracted from hadron momentum spectra. The fact that no such centrality dependence is observed for the chemical decoupling temperature, extracted from the hadron yields measured in these collisions, excludes a similar kinetic interpretation of the chemical decoupling process. We argue that the chemical decoupling data from Au+Au collisions at RHIC can only be consistently understood if the chemical freeze-out process is driven by a phase transition, and that the measured chemical decoupling temperature therefore measures the critical temperature of the quark-hadron phase transition. We propose additional experiments to further test this interpretation.

13 pages. Talk given at the Zimanyi 75 Memorial Workshop on "Hadronic and Quark Matter", Budapest, July 2-4, 2007. To appear in a special volume of The European Physical Journal (Special Topics)

References in corpus (6)

• The QCD transition temperature: results with physical masses in the continuum limit
• The transition temperature in QCD
• Chemical equilibration due to heavy Hagedorn states
• Saturation of Transverse Energy per Charged Hadron and Freeze-Out Criteria in Heavy-Ion Collisions
• Universal chemical freeze-out as a phase transition signature
• Chemical Equilibration at the Hagedorn Temperature

Cited by in corpus (7)

• Divergence-type 2+1 dissipative hydrodynamics applied to heavy-ion collisions
• The strongly coupled quark-gluon plasma created at RHIC
• Causal Viscous Hydrodynamics for Relativistic Heavy Ion Collisions
• System size dependence of the hadronic rescattering effect at energies available at the CERN Large Hadron Collider
• K${}^{\ast }$(892)${}^{\pm }$ resonance production in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Cluster production and the chemical freeze-out in expanding hot dense matter
• Hierarchy of kinetic freeze-out parameters in low energy heavy-ion collisions