Measurement of the azimuthal anisotropy for charged particle production in Pb+Pb collisions at sNN =2.76 TeV and in p+Pb collisions at sNN =5.02 TeV with the ATLAS detector at the LHC

In this work, detailed measurements of the pT, eta and centrality dependence of the flow harmonics vn in Pb+Pb collisions at sNN = 2.76 TeV with the ATLAS detector at the LHC are presented. Consistent values of harmonics v2-v 6 are measured the via event-plane and two-particle correlation methods. Dipolar flow v1 associated with initial dipole asymmetry is measured via two-particle correlations. The long-range correlations in the two-particle correlations such as ridge and the cone are shown to be accounted for by collective flow. Sizable values of the odd harmonics especially v3 are measured that indicate significant event-by-event (EbyE) fluctuations in the initial geometry.;The nature of the initial collision geometry and the hydrodynamic response to it are investigated by measuring the EbyE distributions for harmonics v2-v4, as well as correlations between two and three event-planes phin of different orders. These measurements show the presense of considerable EbyE fluctuations in the initial geometry as well as the importance of non-linear hydrodynamic response of the medium to these fluctuations. By measuring the EbyE vn distributions separately for particles with pT > 1 GeV and with pT ∈ (0.5, 1.0) GeV, the hydrodynamic response is shown to factorize into a function of pT and a function of the initial geometry. The EbyE vn distributions are shown to contain additional information than the multi-particle cumulants.;Two-particle correlations in p+Pb collisions at sNN = 5.02 TeV are measured. Long range correlations are observed along Deltaeta at Delta&phis; ∼ 0 that increase with increasing event-activity. A symmetric long range correlation is also shown to exist at Delta&phis; ∼ pi which is obtained by subtracting out the expected contribution from recoiling dijets. These correlations are shown to be similar to those seen in Pb+Pb collisions suggesting similar physics in both systems.