A Chiral Mean-Field Equation-of-State in UrQMD: Effects on the Heavy Ion Compression Stage

TL;DR

This paper demonstrates that the initial compression in central heavy ion collisions at 1-10A GeV is primarily determined by the equation of state, and introduces a method to incorporate various equations of state into the UrQMD transport model.

Contribution

A new procedure to implement any equation of state in the UrQMD transport model and a comparative analysis of compression dynamics using different models.

Findings

Initial compression depends mainly on the equation of state.

Compression is similar across models when using the same equation of state.

Compression varies significantly with different equations of state.

Abstract

It is shown that the initial compression in central heavy ion collisions at beam energies of $E_\mathrm{lab}=1-10A$~GeV depends dominantly on the underlying equation of state and only marginally on the model used for the dynamical description. To do so, a procedure to incorporate any equation of state in the UrQMD transport model is introduced. In particular we compare the baryon density, temperature and pressure evolution as well as produced entropy in a relativistic ideal hydrodynamics approach and the UrQMD transport model, where the same equation of state is used in both approaches. Not only is the compression similar if the same equation of state is used in either dynamical model, but it also strongly depends on the actual equation of state. These results indicate that the equation of state can be studied with observables which are sensitive to the initial compression phase and maximum compression achieved in heavy ion collisions at these beam energies.