Recently it has become apparent that event-by-event fluctuations in the initial state of hydrodynamical modeling of ultrarelativistic heavy-ion collisions are crucial in order to understand the full centrality dependence of the elliptic flow coefficient $v_2$. In particular, in central collisions the density fluctuations play a major role in generating the spatial eccentricity in the initial state. This raises the question to what degree high-$P_T$ physics, in particular leading-parton energy loss, which takes place in the background of an evolving medium, is sensitive to the presence of the event-by-event density fluctuations in the background. In this work, we report results for the effects of fluctuations on the nuclear modification factor $R_{AA}$ in both central and noncentral $\sqrt{s_{NN}}=200$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider. Two different types of energy-loss models, a radiative model and an elastic model, are considered. In particular, we study the dependence of the results on the assumed spatial size of the density fluctuations and discuss the angular modulation of $R_{AA}$ with respect to the event plane.

• Received 12 May 2011

DOI:https://doi.org/10.1103/PhysRevC.85.044915