1204.1850 (CMS Collaboration)

Azimuthal anisotropy of charged particles at high transverse momenta in
PbPb collisions at sqrt(s[NN]) = 2.76 TeV    [PDF]

CMS Collaboration

The azimuthal anisotropy of charged particles in PbPb collisions at nucleon-nucleon center of mass energy of 2.76 TeV is measured over an extended transverse momentum (pt) range up to approximately 60 GeV. The data cover both the low-pt region associated with hydrodynamic flow phenomena and the high-pt region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. A data sample corresponding to an integrated luminosity of 150 inverse microbarns is analyzed with the CMS detector at the LHC. The anisotropy parameter (v2) of the particles is extracted by correlating charged tracks with respect to the event plane reconstructed 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 v2 values are found to first increase with pt, reaching a maximum around pt = 3 GeV, then gradually decrease to almost zero, with the decline persisting up to at least pt = 40 GeV over the full centrality range measured.

View original: http://arxiv.org/abs/1204.1850