(3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions

TL;DR

This paper models (3+1)-dimensional hydrodynamic expansion in heavy-ion collisions at various energies, incorporating a critical end point in the equation of state, and compares initial conditions from microscopic transport and simple overlap models to identify conditions near the CEP.

Contribution

It introduces a realistic hydrodynamic model with a critical point, using initial conditions from UrQMD, and analyzes the conditions under which the system approaches the critical point during expansion.

Findings

Initial entropy per baryon is similar for both initial conditions.

Expansion paths depend on the equation of state with a critical point.

Certain beam energies lead to a significant system fraction near the critical point.

Abstract

We investigate a (3+1)-dimensional hydrodynamic expansion of the hot and dense system created in head-on collisions of Pb+Pb/Au+Au at beam energies from $5-200A$ GeV. An equation of state that incorporates a critical end point (CEP) in line with the lattice data is used. The necessary initial conditions for the hydrodynamic evolution are taken from a microscopic transport approach (UrQMD). We compare the properties of the initial state and the full hydrodynamical calculation with an isentropic expansion employing an initial state from a simple overlap model. We find that the specific entropy ($S/A$) from both initial conditions is very similar and only depends on the underlying equation of state. Using the chiral (hadronic) equation of state we investigate the expansion paths for both initial conditions. Defining a critical area around the critical point, we show at what beam energies one can expect to have a sizable fraction of the system close to the critical point. Finally, we emphasise the importance of the equation of state of strongly interacting matter, in the (experimental) search for the CEP.