Shengquan Tuo (Vanderbilt University (US))
The higher-order flow anisotropies of charged particles have been systematically studied by the CMS collaboration for PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV. The data were collected with the CMS detector at the LHC in 2010 and 2011. Fourier components of the anisotropic azimuthal distribution, ranging from the third to the sixth component, are obtained using four different analysis techniques: event plane, two- and four-particle correlations, and Lee-Yang Zeros. The results are reported as a function of the particle transverse momentum (pT) for pT = 0.5 - 20 GeV/c and collision centrality. The long-range azimuthal dihadron correlations are extensively studied with a Fourier-decomposition analysis. Using a data driven method, the extracted Fourier coefficients (up to the fifth order) are found to factorize into a product of single-particle azimuthal anisotropies up to pT~3-3.5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Based on the factorization studies, the implications of flow and non-flow effects in the long-range correlations are discussed. Comparison of higher-order harmonics derived from different techniques provides important insight on the initial-state eccentricity fluctuations and helps further constrain the transport properties of the medium.
Collaboration CMS (CERN)