Measurement of inclusive and differential cross sections for single top quark production in association with a W boson at $\sqrt{s}=13~\mathrm{TeV}$

Measurements of the inclusive and normalised differential cross sections are presented for the production of single top quarks in association with a W boson, in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 $\mathrm{fb}^{-1}$. Events containing one muon and one electron in the final state are analysed. For the inclusive measurement, a multivariate discriminant, exploiting the kinematic properties of the events, is used to separate the signal from the dominant t$\bar{\rm{t}}$ background. A measured cross section of $79.2 \pm 0.8 (\mathrm{stat})^{+7.0}_{-7.2} (\mathrm{syst}) \pm 1.1 (\mathrm{lumi}) \ \mathrm{pb}$ is obtained, consistent with predictions of the standard model. For the differential measurements, a fiducial region is defined according to the detector acceptance and the requirement of exactly one b-tagged jet. The resulting distributions are unfolded to particle level and compared with predictions at next-to-leading order in perturbative quantum chromodynamics, with which they agree within uncertainties.