Kernphysikalisches Kolloquium

Location: ITP, Science Campus Riedberg, Max-von-Laue-Str. 1, room 02.116
Time: Thursday, June 21, 2012, 16:30-17:30 (plus 10min for discussion)
Contact: hees@fias.uni-frankfurt.de

Getting particles from a viscous fluid

Denes Molnar (Purdue University)

Comparing hydrodynamic calculations to data inevitably requires the conversion of the fluid to particles. The conversion is ambiguous for viscous fluids because an infinite class of phase space densities can produce the same hydrodynamic variables. It is common to postulate that dissipative phase space density corrections due to shear stress are quadratic in momentum and have the same prefactor for each particle species (a prescription we termed "democratic Grad approach"). Though appealingly simple, this choice ignores microscopic dynamics that governs how close the various particle species are to local equilibrium in the hadron gas. We obtain instead dissipative phase space corrections from the linearized Boltzmann equation, and use those in the Cooper-Frye formalism to convert the fluid to particles. This dynamical freezeout approach will be illustrated using a pion-nucleon gas. Our main finding is that protons are better equilibrated than pions and, therefore, the democratic Grad ansatz overestimates viscous effects on protons.