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 $\sqrt{s_{\mathrm{NN}}}$=2.76 TeV. This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle, where the coefficient for each term, $v_n$, characterizes the magnitude of the anisotropy at a particular angular scale. We extract $v_2-v_6$ via a discrete Fourier analysis of the two-particle $\Delta\phi-\Delta\eta$ correlation with a large $\Delta\eta$ gap ($|\Delta\eta|>2$), and via an event plane method based on the Forward Calorimeter. Significant $v_2-v_6$ values are observed over a broad range in $\pT$, $\eta$ and centrality, and they are found to be consistent between the two methods in the transverse momentum region $\pT<3-4$ GeV. This suggests that the measured $v_2-v_6$ obtained from two-particle correlations at low $\pT$ 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. 
Jiangyong Jia (for the ATLAS Collaboration)
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