Flow and transverse momentum correlations in Pb+Pb and Xe+Xe collisions with ATLAS

Fluctuations of event-wise average transverse momentum, [p_T], and the harmonic flow, v_n, carry important information about initial-state geometry. Collisions of nuclei with large quadrapole deformation are predicted to produce an initial state with enhanced shape and size fluctuations, and result in non-trivial correlation between v_n and [p_T] in the final state. In particular, the v₂ - [p_T] correlations are predicted to be different between collisions of spherical ²⁰⁸Pb and collisions of deformed ¹²⁹Xe. 

This talk presents a new measurement of v_n - [p_T] correlation in √s_NN=5.44 TeV Xe+Xe collisions and compared with Pb+Pb at √s_NN=5.02 TeV for harmonics n=2, 3 and 4 using ATLAS detector. The correlation strength is found to depend strongly on centrality and also on the choice of transverse momentum range of the particles for all harmonics. Comparison with theoretical model calculations are used to shed light on the system-size dependence of this correlation and the influence of deformations. This measurement provides inputs for better understanding of the initial-state nuclear geometry and dynamics of heavy ion collisions.