Microscopic study of freeze-out in relativistic heavy ion collisions at SPS energies

Abstract

The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding systems of heavy nuclei at 160 AGeV/$c$ are analyzed within the microscopic Quark Gluon String Model (QGSM). We found that even for the most heavy systems particle emission takes place from the whole space-time domain available for the system evolution, but not from the thin ''freeze-out hypersurface", adopted in fluid dynamical models. Pions are continuously emitted from the whole volume of the reaction and reflect the main trends of the system evolution. Nucleons in Pb+Pb collisions initially come from the surface region. For both systems there is a separation of the elastic and inelastic freeze-out. The mesons with large transverse momenta, $p_t$, are predominantly produced at the early stages of the reaction. The low $p_t$-component is populated by mesons coming mainly from the decay of resonances. This explains naturally the decreasing source sizes with increasing $p_t$, observed in HBT interferometry. Comparison with S+S and Au+Au systems at 11.6 AGeV/$c$ is also presented.

REVTEX, 26 pages incl. 9 figures and 2 tables, to be published in the Physical Review C

References in corpus (7)

• Microscopic Models for Ultrarelativistic Heavy Ion Collisions
• Excluded volume hadron gas model for particle number ratios in A+A collisions
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• Local Thermodynamical Equilibrium and the Equation of State of Hot, Dense Matter Created in Au+Au Collisions at AGS
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• Non-ideal Particle Distributions from Kinetic Freeze Out Models
• Sensitivity of HBT interferometry to the microscopic dynamics of freeze-out

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