Victoria Zhukova (University of Kansas (US))
Measurements of the azimuthal anisotropy of charged hadrons are presented for PbPb collisions at 2.76 TeV over an extended transverse momentum range up to approximately 60 GeV/c. The data were collected with the CMS detector at the LHC. Utilizing a novel and unique high-pT single-track high-level trigger, the analysis explores the full 2011 PbPb data set corresponding to an integrated luminosity of 150/ub. Anisotropy parameters (v2, v3 and v4) are extracted by correlating charged tracks with the event plane angle reconstructed using the energy deposited in the forward calorimeters. By utilizing the broad coverage of the CMS foward calorimetry, contamination from back-to-back dijets is suppressed. The results presented in this talk significantly improve on the statistical precision of previous v2 measurements for pT> 12 GeV/c, and explore for the first time the harmonic components of the azimuthal dependence in the very high pT region beyond 20 GeV/c. Beyond pT>10 GeV/c, the observed v2 values show a moderate decrease with pT, being consistent with zero only above pT~40 GeV/c and for mid-central (30-60%) collisions. A common trend in the centrality dependence of v2 is observed for particles over a wide range of pT up to approximately 48 GeV/c that is independent of pseudorapditiy, suggesting a potential connection to the initial geometry. These new data can impose quantitative constraints on the details of in-medium parton energy loss models, particularly the influence of the path length and the shape of the interaction region.
Collaboration CMS (CERN)