Measurement of the Correlation Between Flow Harmonics of Different Order in Lead-Lead Collisions at √s̅(NN) = 2.76 TeV with the ATLAS Detector

Correlations between the elliptic or triangular flow coefficients ν_m (m=2 or 3) and other flow harmonics ν_n (n=2 to 5) are measured using \sqrt {s_{NN}}=2.76 TeV Pb+Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 7 μb⁻¹. The ν_m - ν_n correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, ν₃ is found to be anticorrelated with ν₂ and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ε₂ and ε₃. However, it is observed that ν₄ increases strongly with ν₂, and ν₅ increases strongly with both ν₂ and ν₃. The trend and strength of the ν_m-ν_n correlations for n=4 and 5 are found to disagree with ε_m-ε_n correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to ν_n and a nonlinear term that is a function of v_2^2 or of v₂v₃, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to ν₄ and ν₅ are found to be consistent with previously measured event-plane correlations.