## Constraining the viscous freeze-out distribution function with data obtained at the BNL Relativistic Heavy Ion Collider (RHIC)

We investigate the form of the viscous correction to the equilibrium distribution function in the context of a Cooper-Frye freeze-out prescription for viscous hydrodynamic simulations of relativistic heavy ion collisions. The standard quadratic ansatz used by all groups for the case of shear viscosity is found to be disfavored by experimental data for v{sub 4}/(v{sub 2}){sup 2} at the Relativistic Heavy Ion Collider and is unlikely to be correct for the hadron resonance gas present at freeze-out. Instead, data for v{sub 2}(p{sub t}) along with v{sub 4}/(v{sub 2}){sup 2} favor a momentum dependence between linear and quadratic.