Symmetry plane correlations in Pb–Pb collisions at $${\varvec{\sqrt{s_\text {NN}}}} =2.76$$ TeV

A newly developed observable for correlations between symmetry planes, which characterize the direction of the anisotropic emission of produced particles, is mea- sured in Pb–Pb collisions at √sNN = 2.76 TeV with ALICE. This so-called Gaussian Estimator allows for the first time the study of these quantities without the influence of cor- relations between different flow amplitudes. The centrality dependence of various correlations between two, three and four symmetry planes is presented. The ordering of magni- tude between these symmetry plane correlations is discussed and the results of the Gaussian Estimator are compared with measurements of previously used estimators. The results uti- lizing the new estimator lead to significantly smaller cor- relations than reported by studies using the Scalar Product method. Furthermore, the obtained symmetry plane correla- tions are compared to state-of-the-art hydrodynamic model calculations for the evolution of heavy-ion collisions. While the model predictions provide a qualitative description of the data, quantitative agreement is not always observed, partic- ularly for correlators with significant non-linear response of the medium to initial state anisotropies of the collision sys- tem. As these results provide unique and independent infor- mation, their usage in future Bayesian analysis can further constrain our knowledge on the properties of the QCD matter produced in ultrarelativistic heavy-ion collisions.