$R_{\text{AA}}$ and $v_2$ of muons from heavy-quark decays in lead-lead collisions at $\sqrt{s_{_{\text{NN}}}}=2.76$ TeV with the ATLAS detector

ATLAS has measured the production of prompt muons in $\sqrt{s_{_{\text{NN}}}}=2.76$ TeV Pb+Pb collisions $\sqrt{s}=2.76$ TeV $pp$ collisions at the LHC. These muons result primarily from semi-leptoinc decays of heavy flavor hadrons. The measurements are performed over the transverse momentum and pseudorapidity ranges, $4<p_{\text{T}}<14$ GeV and $|\eta|<1$ and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and mis-reconstructed muons are statistically estiamted using a template fitting procedure. The prompt muon differential cross-sections and per-event yields are measured in $pp$ and Pb+Pb collisions, respectively. Nuclear modification factors, $R_{\text{AA}}$, are measured as a function of $p_{\text{T}}$ in the different centrality intervals. They are observed to be independent of $p_T$ within uncertainties and to be less than unity which indicates suppression of the production of prompt muons in Pb+Pb collisions. For the most central interval measured (0–10%), $R_{\text{AA}}\approx0.4$. The prompt muon $v_2$ was measured using the event plane technique with the the elliptic event plane angle measured using forward calorimeters that cover $3.2<|\eta|<4.9$. Significant $v_2$ values are observed in all centrality and $p_{\text{T}}$ intervals. They vary, at most, slowly with $p_{\text{T}}$ and show a significant dependence on centrality characteristic of elliptic flow.