Measurement of flow harmonics with multi-particle cumulants in Pb+Pb collisions at √sNN =2.76 TeV with the ATLAS detector

ATLAS measurements of the azimuthal aniso- tropy in lead–lead collisions at √sNN = 2.76 TeV are shown using a dataset of approximately 7 μb−1 collected at the LHC in 2010. The measurements are performed for charged parti- cles with transverse momenta 0.5 < pT < 20 GeV and in the pseudorapidity range |η| < 2.5. The anisotropy is character- ized by the Fourier coefficients, vn, of the charged-particle azimuthal angle distribution for n = 2–4. The Fourier coef- ficients are evaluated using multi-particle cumulants calcu- lated with the generating function method. Results on the transverse momentum, pseudorapidity and centrality depen- dence of the vn coefficients are presented. The elliptic flow, v2, is obtained from the two-, four-, six- and eight-particle cumulants while higher-order coefficients, v3 and v4, are determined with two- and four-particle cumulants. Flow har- monics vn measured with four-particle cumulants are sig- nificantly reduced compared to the measurement involving two-particle cumulants. A comparison to vn 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 ini- tial spatial geometry and its fluctuations fail to describe the flow fluctuations measurements.