Measurement of Flow Harmonics with Multi-Particle Cumulants in Pb + Pb Collisions at √{S_{NN}} = 2.76 TeV with the ATLAS Detector

ATLAS measurements of the azimuthal anisotropy 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 particles with transverse momenta 0.5 < p_T < 20 GeV and in the pseudorapidity range |η| < 2.5. The anisotropy is characterized by the Fourier coefficients, v_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_n 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 harmonics v(n) measured with four-particle cumulants are significantly reduced compared to the measurement involving two-particle cumulants. A comparison to v_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 multiparticle 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.