Recent ATLAS measurements of correlations in Pb+Pb and Xe+Xe collisions

Abstract

ATLAS measurements of flow harmonics, $v_{\rm n}$, and their fluctuations in Pb+Pb and Xe+Xe collisions at the Large Hadron Collider (LHC), covering a wide range of transverse momenta, pseudorapidity and collision centrality, are presented. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV and Pb+Pb collisions at 5.02 TeV. The flow harmonics are measured using the two-particle correlations, multi-particle cumulants, and scalar product methods. Similar $p_{\rm T}$ and centrality dependence of $v_{\rm n}$ values is observed for both systems. A new universal scaling of harmonics of different orders leading to $p_{\rm T}$ and even centrality independence is described. Measurements of longitudinal flow decorrelations involving two- and four-particle correlations for $v_{\rm 2}$ and $v_{\rm 3}$ in Xe+Xe and Pb+Pb collisions are briefly mentioned. Some results for event-by-event correlations between harmonics of different orders, studied with three- and four-particle mixed-harmonic cumulants, are shown. Contributions to these correlations from “centrality fluctuations” are also discussed. Finally the measurement of elliptic and triangular flow of muons from charm and bottom hadron decays in 5.02 TeV Pb+Pb collisions is presented.