Characterizing the hydrodynamic response to the initial conditions

In hydrodynamics, the momentum distribution of particles at the end of the evolution is completely determined by initial conditions. We study quantitatively to what extent anisotropic flow vn is determined by predictors such as the initial eccentricity εn in a set of realistic simulations, and we also show the importance of nonlinear terms in order to correctly predict v4. This knowledge will be important for making a more direct link between experimental observables and hydrodynamic initial conditions, the latter being poorly constrained at present.