Hadronic dissipative effects on elliptic flow in ultrarelativistic heavy-ion collisions

We study the elliptic flow coefficient v2(η,b) in Au + Au collisions at s=200AGeV as a function of pseudorapidity η and impact parameter b. Using a hybrid approach which combines early ideal fluid dynamical evolution with late hadronic rescattering, we demonstrate strong dissipative effects from the hadronic rescattering stage on the elliptic flow. With Glauber model initial conditions, hadronic dissipation is shown to be sufficient to fully explain the differences between measured v2 values and ideal hydrodynamic predictions. Initial conditions based on the Color Glass Condensate model generate larger elliptic flow and seem to require additional dissipation during the early quark-gluon plasma stage in order to achieve agreement with experiment.