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arXiv · 1407.6413

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

Zack Wolff·Denes Molnar
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Abstract

Comparing hydrodynamic simulations to heavy-ion data inevitably requires the conversion 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 solving the 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 independent of particle dynamics. Solutions are calculated analytically for a massless gas and numerically for both a pion-nucleon gas and for the general case of a hadron resonance gas. We find that the momentum dependence of the corrections in all systems investigated is best fit by a power close to 3/2 rather than the typically used quadratic ansatz. The effects on harmonic flow coefficients $v_2$ and $v_4$ are substantial, and should be taken into account when extracting medium properties from experimental data.

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Zack Wolff, Denes Molnar. 2014-07-24. Self-consistent Cooper-Frye freeze-out of a viscous fluid to particles. https://doi.org/10.1088/1742-6596/535/1/012020

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