Collective dynamics of heavy ion collisions in ATLAS

An overview of the latest ATLAS experiment measurements of collective behaviour in a variety of collision systems, including 13 TeV $pp$, 5.44 TeV Xe+Xe and 5.02 TeV Pb+Pb collisions is presented. The results shown include measurements of $v_n$-mean $p_T$ correlations and longitudinal flow decorrelations in Xe+Xe and Pb+Pb collisions, which carry important information about the initial-state geometry of the Quark-Gluon Plasma; heavy flavour flow harmonics testing the quark energy loss mechanism in QGP; and measurements of the sensitivity of collective behaviour in $pp$ collisions to the presence of jets, which provide insight on the role of semi-hard processes in the origin of the flow phenomena in small systems. These results provide stringent tests of the theoretical understanding of the initial state in heavy ion collisions.