Correlations between flow and transverse momentum in Pb+Pb and Xe+Xe collisions with ATLAS

The measurement of the correlation between flow harmonics $v_n$ and average transverse momentum $p_\mathrm{T}$ for n = 2, 3 and 4 with the ATLAS detector at the LHC is presented, based on 3$\mu \mathrm{b}^{-1}$ Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV and 22$\mu \mathrm{b}^{-1}$ Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. This correlation is characterized by the Pearson correlation coefficient, $\rho(v_n^2,[p_\mathrm{T}])$, which quantifies the strength of the correlation between $v_n^2$ and event-by-event average $p_\mathrm{T}$, $[p_\mathrm{T}]$. The results are obtained for several ranges in $p_\mathrm{T}$ and pseudorapidity $\eta$ and they are also compared between two different methods to characterize the event activity: the number of charged particles at mid-rapidity and transverse energy at the forward pseudorapidity. The strength of the correlation is found to depend on centrality, $p_\mathrm{T}$ and $\eta$ range, harmonic number $n$, and the collisions systems. Significant differences are observed between results using the two different event class definitions, indicating a strong influence of the centrality fluctuations on these observables. Current theoretical models describe some of the observed centrality dependent trends qualitatively but cannot describe the data quantitatively. This measurement provides insights on the initial-state geometry and final-state dynamics in heavy ion collisions.