High-pT π0 production with respect to the reaction plane in Au+Au collisions at sNN=200 GeV

Abstract

Measurements of the azimuthal anisotropy of high-pT neutral pion (π0) production in Au+Au collisions at sNN=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of π0 mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v2) of the angular distributions are presented as a function of π0 transverse momentum (pT) for different bins in collision centrality. Measured reaction plane dependent π0 yields are used to determine the azimuthal dependence of the π0 suppression as a function of pT, RAA(Δ,pT). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the π0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis. © 2009 The American Physical Society.