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Extracting the equation of state from a microscopic non-equilibrium model

C. Spieles, A. Dumitru, S. A. Bass, M. Bleicher, J. Brachmann, M. Brandstetter, C. Ernst, L. Gerland, J. Konopka, S. Soff, H. Weber, L. A. Winckelmann, J. Maruhn, H. Stoecker, W. Greiner

nucl-tharXiv:nucl-th/9606030

Abstract

We study the thermodynamic properties of infinite nuclear matter with the Ultrarelativistic Quantum Molecular Dynamics (URQMD), a semiclassical transport model, running in a box with periodic boundary conditions. It appears that the energy density rises faster than T4 at high temperatures of T≈ 200-300~MeV. This indicates an increase in the number of degrees of freedom. Moreover, We have calculated direct photon production in Pb+Pb collisions at 160~GeV/u within this model. The direct photon slope from the microscopic calculation equals that from a hydrodynamical calculation without a phase transition in the equation of state of the photon source.

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