Self-consistent Cooper-Frye freeze-out of a viscous fluid to particles

Wolff, Z. and Molnár, Dénes (2014) Self-consistent Cooper-Frye freeze-out of a viscous fluid to particles. JOURNAL OF PHYSICS-CONFERENCE SERIES, 535. ISSN 1742-6588

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Abstract

Comparing hydrodynamic simulations to heavy-ion data inevitably requires theconversion of the fluid to particles. This conversion, typically done in the Cooper-Frye formalism,is ambiguous for viscous fluids. We compute self-consistent phase space corrections by solvingthe linearized Boltzmann equation and contrast the solutions to those obtained using the ad-hoc“democratic Grad” ansatz typically employed in the literature where coefficients are independentof particle dynamics. Solutions are calculated analytically for a massless gas and numericallyfor both a pion-nucleon gas and for the general case of a hadron resonance gas. We find that themomentum dependence of the corrections in all systems investigated is best fit by a power closeto 3/2 rather than the typically used quadratic ansatz. The effects on harmonic flow coefficientsv2 and v4 are substantial, and should be taken into account when extracting medium propertiesfrom experimental data.

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