Equilibrium and non-equilibrium effects in nucleus-nucleus collisions
Abstract
Local thermal and chemical equilibration is studied for central A+A collisions at 10.7-160 AGeV in the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). The UrQMD model exhibits strong deviations from local equilibrium at the high density hadron-string phase formed during the early stage of the collision. Equilibration of the hadron-resonance matter is established in the central cell of volume V=125 fm3 at later stages, t>=10 fm/c, of the resulting quasi-isentropic expansion. The thermodynamical functions in the cell and their time evolution are presented. Deviations of the UrQMD quasi-equilibrium state from the statistical mechanics equilibrium are found. They increase with energy per baryon and lead to a strong enhancement of the pion number density as compared to statistical mechanics estimates at SPS energies.
- Publication:
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Physics Letters B
- Pub Date:
- July 1999
- DOI:
- 10.1016/S0370-2693(99)00692-9
- Bibcode:
- 1999PhLB..459..660B
- Keywords:
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- HEAVY ION COLLISIONS;
- QMD MODEL;
- LOCAL THERMODYNAMICAL EQUILIBRIUM;
- EQUATION OF STATE;
- NON-EQUILIBRIUM EFFECTS