Azimuthal anisotropy of charged particles at high transverse momenta in Pb-Pb collisions at √s NN=2.76TeV

The azimuthal anisotropy of charged particles in Pb-Pb collisions at √s NN=2.76TeV is measured with the CMS detector at the LHC over an extended transverse momentum (p T) range up to approximately 60GeV/c. The data cover both the low-p T region associated with hydrodynamic flow phenomena and the high-p T region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v 2) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0-60% most-central events, the observed v 2 values are found to first increase with p T, reaching a maximum around p T=3GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least p T=40GeV/c over the full centrality range measured. © 2012 CERN. Published by the American Physical Society.