Jozsó's Legacy: Chemical and kinetic freeze-out in heavy-ion collisions |
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Authors: | U Heinz G Kestin |
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Institution: | (1) Department of Physics, The Ohio State University, Columbus, OH 43210, USA;(2) Physics Department, Theory Division, CERN, 1211 Geneva 23, Switzerland |
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Abstract: | We review J. Zimányi'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 Zimányi'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. |
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Keywords: | |
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