| The azimuthal anisotropy of charged particles is an important feature of the hot and dense medium produced in heavy ion collisions. In non-central nucleus-nucleus collisions, the maximum particle density defines an event plane which is an approximation to the participant plane. The participant plane reflects the direction of the maximum of the pressure gradient set up by the participating nucleons. The initial nuclear overlap region is spatially asymmetric with an "almond-like" shape. This spatial asymmetry is reflected in the momentum distribution of the particles with respect to the event plane. The anisotropy is quantified in terms of a Fourier expansion of the observed particle yields relative to the event-by-event orientation of the participant plane. The second coefficient of the expansion, upsilon 2, often referred to as "elliptic flow", carries information on the early collision dynamics when measured in the low-pT domain. A similar signal of a different origin is observed in the high- pT regime and is associated with parton energy loss in the presence of the medium. In this work the azimuthal anisotropy of charged hadrons is determined over an extended transverse momentum (p t) range up to approximately 60 GeV/c in PbPb collisions at sNN = 2.76 TeV, covering both the low-pt region associated with hydrodynamic flow phenomena and the high-pt region, pt > 12 GeV/c, where the anisotropies reflect the path-length dependence of parton energy loss in the created medium. |
