Measurement of the correlation between flow harmonics of different order in lead-lead collisions at √s[subscript NN] = 2.76 TeV with the ATLAS detector

Abstract

Correlations between the elliptic or triangular flow coefficients v[subscript m] (m = 2 or 3) and other flow harmonics v[subscript n] (n = 2 to 5) are measured using √s[subscript 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[superscript −1]. The v[subscript m]−v[subscript 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, v[subscript 3] is found to be anticorrelated with v[subscript 2] and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ε[subscript 2] and ε[subscript 3]. However, it is observed that v[subscript 4] increases strongly with v[subscript 2], and v[subscript 5] increases strongly with both v[subscript 2] and v[subscript 3]. The trend and strength of the v[subscript m]−v[subscript n] correlations for n = 4 and 5 are found to disagree with ε[subscript m]−ε[subscript 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[subscript n] and a nonlinear term that is a function of v[2 over 2] or of v[subscript 2]v[subscript 3], as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to v[subscript 4] and v[subscript 5] are found to be consistent with previously measured event-plane correlations.