Measurement of the centrality and pseudorapidity dependence of the integrated elliptic flow in lead-lead collisions at sqrt(sNN) = 2.76 TeV with the ATLAS detector

The elliptic flow of charged particles integrated over their transverse momenta has been measured in Pb+Pb collisions at sqrt(sNN)=2.76 TeV with the ATLAS detector at the LHC. The anisotropy parameter, v2, has been determined using the event plane method in the pseudorapidity range |eta|< 2.5. A special track reconstruction method was applied in the analysis of data taken in 2010 without a magnetic field in order to explore the range of very low transverse momentum, pT, thus reducing the uncertainty in the v2 integrated over pT. Other track reconstruction methods have been used for consistency checks and to provide measurements directly comparable to previously published results. The centrality dependence of the integrated v2, spanning the range of 0-80% of most central Pb+Pb collisions, is compared to other LHC measurements obtained with a higher pT threshold. A weak pseudorapidity dependence of the integrated elliptic flow is observed for central collisions, and a small decrease when moving away from mid-rapidity can be seen only in peripheral collisions. The energy dependence of v2 in the rest frame of one of the colliding nuclei is discussed in comparison to the lower energy RHIC data.