Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV

This note documents the muon identification performance obtained by the ATLAS experiment between 2015 and 2018 during the LHC Run 2, corresponding to 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV. The increased instantaneous luminosity delivered by the LHC over this period demanded a re-optimization of the criteria for the identification of prompt muons. Improved and newly-developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of statistically large samples of $Z\to\mu\mu$ and $J/\psi\to\mu\mu$ decays, and the minimization of systematic uncertainties, allow for the measurement of the efficiencies of muon identification, association to the primary-vertex, and isolation criteria with accuracy at the per mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several TeV, and across the full detector acceptance of $|\eta|<2.7$.