Measurement of elliptic and higher order flow from ATLAS experiment at the LHC

We present a differential measurement of the azimuthal anisotropy of charged hadron production in Pb+Pb collisions at √S_NN = 2.76 TeV. This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle, where the coefficient for each term, νn, characterizes the magnitude of the anisotropy at a particular angular scale. We extract ν2-ν6 via a discrete Fourier analysis of the two-particle δφ-δη correlation with a large δη gap (|δη| > 2), and via an event-plane method based on the forward calorimeter. Significant ν2ν6 values are observed over a broad range in P_T, η and centrality, and they are found to be consistent between the two methods in the transverse momentum region P_T < 34 GeV. This suggests that the measured v2v6 obtained from two-particle correlations at low pT with a large δη gap are consistent with the collective response of the system to the initial-state geometry fluctuations, and is not the result of jet fragmentation or resonance decay.