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 root s(NN) = 2.76 TeV. This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle, where the coefficient for each term, nu(n), characterizes the magnitude of the anisotropy at a particular angular scale. We extract nu(2)-nu(6) via a discrete Fourier analysis of the two-particle Delta phi-Delta eta correlation with a large Delta(eta) gap (vertical bar Delta eta vertical bar > 2), and via an event-plane method based on the forward calorimeter. Significant nu(2)-nu(6) values are observed over a broad range in p(T), eta and centrality, and they are found to be consistent between the two methods in the transverse momentum region p(T) < 3-4 GeV. This suggests that the measured nu(2)-nu(6) obtained from two-particle correlations at low p(T) with a large Delta(eta) 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.