The elliptic flow of muons from the decay of charm and bottom hadrons is measured in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ using a data sample with an integrated luminosity of $150{\mathrm{pb}}^{-1}$ recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4–7 GeV and pseudorapidity range $|\eta |<2.4$. A significant nonzero elliptic anisotropy coefficient $v_2$ is observed for muons from charm decays, while the $v_2$ value for muons from bottom decays is consistent with zero within uncertainties.

• Received 5 September 2019
• Revised 29 November 2019
• Accepted 22 January 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.082301

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