Measurement of the correlation between flow harmonics of different order in lead-lead collisions at √s_NN = 2.76 TeV with the ATLAS detector

Correlations between the elliptic or triangular flow coefficients v_m (m = 2 or 3) and other flow harmonics v_n (n = 2 to 5) are measured using √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 v_m-v_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, v₃ is found to be anticorrelated with v₂ and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ∊₂ and ∊₃. However, it is observed that v₄ increases strongly with v₂, and v₅ increases strongly with both v₂ and v₃. The trend and strength of the v_m-v_n correlations for n = 4 and 5 are found to disagree with ∊_m-∊_n correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to v_n and a nonlinear term that is a function of v₂² 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 v₄ and v₅ are found to be consistent with previously measured event-plane correlations.