Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in Pb+Pb collisions at $\sqrt {s_{NN}}$ = 5.02 TeV with the ATLAS detector
Phys.Lett.B 807 (2020) 135595 , 2020.
The ATLAS collaboration

Abstract (data abstract)
CERN-LHC. Azimuthal anisotropies of muons from charm and bottom hadron decays are measured in Pb+Pb collisions at 5.02 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2018 with integrated luminosities of 0.5 nb^{-1} and 1.4 nb^{-1}, respectively. The kinematic selection for heavy-flavor muons requires transverse momentum 4 <pT< 30 GeV and pseudorapidity |η|< 2.0. The dominant sources of muons in this pT 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 tracking and 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 pT 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 (v2) and triangular (v3) 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.

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