Dissecting the role of initial collision geometry for jet quenching observables in relativistic heavy ion collisions

The observation of large azimuthal anisotropy or v2 for hadrons above pT>5GeV/c in Au+Au collisions at √snn=200GeV has been a longstanding challenge for jet quenching models based on perturbative QCD (pQCD). Using a simple jet absorption model, we seek to clarify the situation by exploring in detail how the calculated v2 varies with choices of the collision geometry, as well as choices of the path-length dependence and thermalization time τ0 in the energy-loss formula. Besides the change of eccentricity owing to distortion from gluon saturation or event-by-event fluctuation, we find that the v2 is also sensitive to the centrality dependence of multiplicity and the relative size between the matter profile and the jet profile. We find that the v2 calculated for the naive quadratic path-length dependence of energy loss, even including eccentricity fluctuation and the gluon saturation, is not enough to describe the experimental data at high pT (∼6GeV/c) in Au+Au collisions. However, it can match the full centrality dependence of v2 data if higher-power path-length dependence of energy loss is allowed. We also find that the calculated v2 is sensitive to the assumption of the early time dynamics but generally increases with τ0, opposite to what one expects for elliptic flow. This study attests to the importance of confining the initial geometry, possibly by combining jet quenching v2 with elliptic flow and other jet quenching observables, for proper interpretation of the experimental data.