Measurement of the elliptic anisotropy of charged particles produced in PbPb collisions atâ‹ısNN=2.76 TeV

The anisotropy of the azimuthal distributions of charged particles produced in √ s NN = 2.76 TeV PbPb collisions is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter, v 2 , defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two-and four-particle cumulants, and Lee-Yang zeros. The anisotropy is presented as a function of transverse momentum (p T), pseudorapidity (η) over a broad kinematic range, 0.3 < p T < 20 GeV/c, |η| < 2.4, and in 12 classes of collision centrality from 0 to 80%. The results are compared to those obtained at lower center-of-mass energies, and various scaling behaviors are examined. When scaled by the geometric eccentricity of the collision zone, the elliptic anisotropy is found to obey a universal scaling with the transverse particle density for different collision systems and center-of-mass energies.