Measurement of flow harmonics with multi-particle cumulants in Pb+Pb collisions at √s[subscript NN] = 2.76 TeV with the ATLAS detector

Abstract

ATLAS measurements of the azimuthal anisotropy in lead–lead collisions at √s[subscript NN] = 2.76 TeV are shown using a dataset of approximately 7 μ b [superscript −1] collected at the LHC in 2010. The measurements are performed for charged particles with transverse momenta \(0.5 GeV and in the pseudorapidity range |η|<2.5 . The anisotropy is characterized by the Fourier coefficients, v [subscript n] , of the charged-particle azimuthal angle distribution for n=2 –4. The Fourier coefficients are evaluated using multi-particle cumulants calculated with the generating function method. Results on the transverse momentum, pseudorapidity and centrality dependence of the v [subscript n] coefficients are presented. The elliptic flow, v [subscript 2], is obtained from the two-, four-, six- and eight-particle cumulants while higher-order coefficients, v [subscript 3] and v [subscript 4], are determined with two- and four-particle cumulants. Flow harmonics vn measured with four-particle cumulants are significantly reduced compared to the measurement involving two-particle cumulants. A comparison to v [subscript n] measurements obtained using different analysis methods and previously reported by the LHC experiments is also shown. Results of measurements of flow fluctuations evaluated with multi-particle cumulants are shown as a function of transverse momentum and the collision centrality. Models of the initial spatial geometry and its fluctuations fail to describe the flow fluctuations measurements.