Measurement of tW production in the semileptonic channel in pp collisions at $\sqrt{s}=13~\mathrm{TeV}$

A measurement of the associated production of a single top quark and a W boson in the final states with an electron or muon and jets using pp collisions with $\sqrt{s}=13~\mathrm{TeV}$ collected by the CMS detector at the CERN LHC is presented. The data used correspond to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. This result is the first observation of the tW process in the final states containing a muon or electron and jets, with an observed significance clearly exceeding 5 standard deviations. The measured signal strength is $\mu = 1.24\pm0.18$, consistent with unity. The inclusive cross section is determined to be $89\pm4$ (stat) $\pm~12$ (syst)$~\mathrm{pb}$.