Seminar in Hadronic Physics

Mapping the hydrodynamic response to the initial geometry in heavy-ion collisions

Matthew Luzum

McGill University

We investigate how the initial geometry of a heavy-ion collision is transformed into final flow observables by solving event-by-event ideal hydrodynamics with realistic fluctuating initial conditions. We study quantitatively to what extent anisotropic flow (v_n) is determined by the initial eccentricity e_n for a set of realistic simulations, and we discuss which definition of e_n gives the best estimator of v_n. We similarly study the importance of additional properties of the initial state. For example, we show that in order to correctly predict v4 and v5 for non-central collisions, one must take into account nonlinear terms proportional to e₂² and e₂e₃, respectively. We find that it makes no difference whether one calculates the eccentricities over a range of rapidity, or in a single slice at z = 0, nor is it important whether one uses an energy or entropy density weight. 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.