Cooper-Frye Negative Contributions in a Coarse-Grained Transport Approach

FAIR Next Generation ScientistS 2014

Oliinychenko, D.^1,3 ; Huovinen, P.^1,2 ; Petersen, H.^1,2

Frankfurt Institute for Advanced Studies, Frankfurt am Main

D-60438, Germany^1

Institut für Theoretische Physik, Goethe-Universität, Frankfurt am Main

D-60438, Germany^2

Bogolyubov Institute for Theoretical Physics, Kiev

03680, Ukraine^3

关键词: Coarse-grained;    Collision energies;    Equilibrium distribution functions;    Heavy ion collision;    Mid-rapidity;    Positive definite;    Relativistic hydrodynamics;    System evolution;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/599/1/012017/pdf
DOI  :  10.1088/1742-6596/599/1/012017

来源: IOP

【 摘 要 】

Many models of heavy ion collisions employ relativistic hydrodynamics to describe the system evolution at high densities. The Cooper-Frye formula is applied in most of these models to turn the hydrodynamical fields into particles. However, the number of particles obtained from the Cooper-Frye formula is not always positive-definite. Physically negative contributions of the Cooper-Frye formula are particles that stream backwards into the hydrodynamical region. We quantify the Cooper-Frye negative contributions in a coarse-grained transport approach, which allows to compare them to the actual number of underlying particles crossing the transition hypersurface. It is found that the number of underlying inward crossings is much smaller than the one the Cooper-Frye formula gives under the assumption of equilibrium distribution functions. The magnitude of Cooper-Frye negative contributions is also investigated as a function of hadron mass, collision energy in the range ELab = 5 - 160A GeV, and collision centrality. The largest negative contributions we find are around 13% for the pion yield at midrapidity at ELab = 20A GeV collisions.