Measurement of the cross-section for the production of a $W$ boson in association with $b$-jets in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

This paper presents a measurement of the production cross-section of a $W$ boson associated with one or two jets, where at least one jet originates from a $b$-quark. The data are collected with the ATLAS detector at the LHC in proton-proton collisions at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 140 fb${}^{\text{-}1}$. Differential cross-sections are presented as a function of the transverse momentum of the $b$-jet for both the electron and muon decay modes of the $W$ boson. The results corrected for all detector effects are presented in a fiducial region defined with basic lepton and jet kinematics, and compared with theoretical predictions. The averaged fiducial cross-section of $W+b$-jets for the electron and muon channels is measured to be $16.6\pm 1.9$ pb, which is consistent with the next-to-leading-order QCD prediction of $16.8\pm 2.3$ pb. The relative precision of this measurement is improved by approximately a factor of two compared with the previous ATLAS measurement at $\sqrt{s}=7$ TeV.