Measurement of heavy flavor production and azimuthal anisotropy in small and large systems with ATLAS

Measurements of heavy flavor hadron production and their correlations in A+A collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in the QGP. From this perspective, the same measurements in $p$+A collisions thus serve as a necessary baseline for understanding the observations in A+A collisions. Additionally, detailed studies of the azimuthal anisotropy for heavy flavor hadrons in $p$+A may help address the question of whether the observed long-range ``ridge'' correlation arises from hard or semi-hard processes, or if it is the result of mechanisms unrelated to the initial hardness scale. This talk presents ATLAS measurements of heavy flavor production, via their semi-leptonic decay to muons in $\sqrt{s_\mathrm{NN}} = 2.76$ TeV Pb+Pb and $pp$ collisions, and via identified prompt $D$ mesons in $\sqrt{s_\mathrm{NN}} = 8.16$ TeV $p$+Pb collisions. Heavy flavor muon yields are observed to be strongly suppressed in Pb+Pb collisions compared to that in $pp$ collisions. On the other hand, the prompt $D$ meson production in $p$+Pb collisions shows no obvious modification compared to the theoretical predictions for $pp$ collisions, indicating relatively small cold nuclear matter effects for $D$ meson production. The $p_{\mathrm{T}}$ and centrality dependence of flow harmonics $v_2$--$v_4$ associated with heavy-flavor muons in Pb+Pb are also presented. The measured $v_2$ decreases over the $p_{\mathrm{T}}$ range of 4--14 GeV, and shows a systematic variation with centrality that was observed in other $v_2$ measurements. The anisotropy measurements are extended to 8.16 TeV $p$+Pb collisions, where the azimuthal modulations of heavy-flavor muons, prompt $D$ mesons and J/$\psi$ are studied using two-particle correlations. The statistical significance of the presence or absence of long range correlations involving heavy flavor production in $p$+Pb events is quantified.