Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in Pb+Pb collisions at TeV with the ATLAS detector

Azimuthal anisotropies of muons from charm and bottom hadron decays are measured in Pb+Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{0.25em}{0ex}}\text{TeV}$. The data were collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2018 with integrated luminosities of $0.5\phantom{\rule{0.25em}{0ex}}{\mathrm{nb}}^{-1}$ and $1.4\phantom{\rule{0.25em}{0ex}}n{b}^{-1}$, respectively. The kinematic selection for heavy-flavor muons requires transverse momentum $4<{p}_{T}<30\phantom{\rule{0.25em}{0ex}}\text{GeV}$ and pseudorapidity $|\eta |<2.0$. The dominant sources of muons in this ${p}_{T}$ range are semi-leptonic decays of charm and bottom hadrons. These heavy-flavor muons are separated from light-hadron decay muons and punch-through hadrons using the momentum imbalance between the measurements in the tracking detector and in the muon spectrometers. Azimuthal anisotropies, quantified by flow coefficients, are measured via the event-plane method for inclusive heavy-flavor muons as a function of the muon ${p}_{T}$ and in intervals of Pb+Pb collision centrality. Heavy-flavor muons are separated into contributions from charm and bottom hadron decays using the muon transverse impact parameter with respect to the event primary vertex. Non-zero elliptic (${v}_{2}$) and triangular (${v}_{3}$) flow coefficients are extracted for charm and bottom muons, with the charm muon coefficients larger than those for bottom muons for all Pb+Pb collision centralities. The results indicate substantial modification to the charm and bottom quark angular distributions through interactions in the quark-gluon plasma produced in these Pb+Pb collisions, with smaller modifications for the bottom quarks as expected theoretically due to their larger mass.