Comparative analysis of the harmonic flow measured by the event plane and two-particle correlation methods in lead-lead collisions at sqrt(s_NN)=2.75 TeV using the ATLAS detector at LHC.

Differential measurements of charged particle azimuthal anisotropy will be presented for Pb+Pb collisions at √s_NN=2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb−1. This anisotropy is characterized via a Fourier expansion of the distribution of particles in azimuthal angle measured with respect to the event reaction plane. The coefficients v_n, representing the magnitude of the harmonic flow at a particular angular scale, are measured as a function of transverse momentum (0.5 < pT < 20 GeV), pseudorapidity (|η| < 2.5) and centrality. The measurement of the harmonic values up to n=6 obtained via the two particle correlation method are compared with those from the event plane analysis. The behavior shown by this comparison suggests a connection between these observables and fluctuations in the geometry of the initial state. A large pseudorapidity gap between the tracking system and forward calorimeters is seen to significantly reduce contributions from short-range non-flow effects, permitting analyses of the collective flow component of the harmonic coefficients.