The observation of large azimuthal anisotropy or $v_2$ for hadrons above $p_T>5$ GeV/$c$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{nn}}}=200$ GeV 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 $v_2$ varies with choices of the collision geometry, as well as choices of the path-length dependence and thermalization time ${\tau }_0$ 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 $v_2$ 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 $v_2$ 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 $p_T$ ($~$$6$ GeV/$c$) in $\mathrm{Au}+\mathrm{Au}$ collisions. However, it can match the full centrality dependence of $v_2$ data if higher-power path-length dependence of energy loss is allowed. We also find that the calculated $v_2$ is sensitive to the assumption of the early time dynamics but generally increases with ${\tau }_0$, opposite to what one expects for elliptic flow. This study attests to the importance of confining the initial geometry, possibly by combining jet quenching $v_2$ with elliptic flow and other jet quenching observables, for proper interpretation of the experimental data.

• Received 15 June 2010

DOI:https://doi.org/10.1103/PhysRevC.82.024902