Speaker
Description
The theoretical description of heavy ion collisions based on hydrodynamics allows to investigate the Equation of State (EoS) of strongly-interacting matter. This benefit comes with assumptions, such as rapid thermalization [2], negligible backflow to hydrodynamics (also known as negative Cooper-frye contributions), existence of a sharp freeze-out hypersurface and possibility to determine it aposteriori from only hydrodynamical evolution. At low collision energies, as well as in event-by-event simulations, these assumptions are violated, in particular the backflow becomes large [1].
In this talk a simple method is suggested to partially relax the above mentioned assumptions, while keeping the same advantages: in a pure transport simulation forced thermalization is performed in regions with high energy density. The backflow is then automatically taken into account by the transport, the transition hypersurface is determined dynamically and, most remarkably, it is possible to plug in an arbitrary EoS, with or without phase transition, directly in the transport. Instead of a sharp freeze-out hypersurface a gradual transition can be constructed by assigning space-time dependent probabilities for particles to be thermalized.
We demonstrate the suggested method using the SMASH (Simulating Multiple Accelerated Strongly-interacting Hadrons) hadronic transport approach and show that forced thermalization leads to a longer lifetime of the system, increases the multiplicity of strange particles and affects anisotropic flow. Finally, the outcome of dynamically coupled approach with different EoS is compared - hadron gas EoS versus chiral EoS with the first order phase transition.
[1] D. Oliinychenko, P. Huovinen, H. Petersen, "Systematic Investigation of Negative Cooper-Frye Contributions in Heavy Ion Collisions Using Coarse-grained Molecular Dynamics", Phys.Rev. C91 (2015) no.2, 024906
[2] D. Oliinychenko, H. Petersen, "Deviations of the Energy-Momentum Tensor from Equilibrium in the Initial State for Hydrodynamics from Transport Approaches",
Phys.Rev. C93 (2016) no.3, 034905
