Effects of viscosity on the mapping of initial to final state in heavy ion collisions

We investigate the correlation between various aspects of the initial geometry of heavy ion collisions at the BNL Relativistic Heavy Ion Collider energies and the final anisotropic flow, using v-USPhydro, a 2+1 event-by-event viscous relativistic hydrodynamical model. We test the extent of which shear and bulk viscosity affect the prediction of the final flow harmonics, vn, from the initial eccentricities, Én. We investigate in detail the flow harmonics v1 through v5 where we find that v1,v4, and v5 are dependent on more complicated aspects of the initial geometry that are especially important for the description of peripheral collisions, including a nonlinear dependence on eccentricities as well as a dependence on shorter-scale features of the initial density. Furthermore, we compare our results to previous results from NeXSPheRIO, a 3+1 relativistic ideal hydrodynamical model that has a nonzero initial flow contribution, and find that the combined contribution from 3+1 dynamics and nonzero, fluctuating initial flow decreases the predictive ability of the initial eccentricities, in particular for very peripheral collisions, but also disproportionately in central collisions.