The inclusive cross-section for the associated production of a $W$ boson and top quark is measured using data from proton-proton collisions at $\sqrt{ s}={ 13}$ TeV. The dataset corresponds to an integrated luminosity of 3.2 fb$^{ -1}$, and was collected in 2015 by the ATLAS detector at the Large Hadron Collider at CERN. Events are selected requiring two opposite sign isolated leptons and at least one jet; they are separated into signal and control regions based on their jet multiplicity and the number of jets that are identified as containing $b$ hadrons. The $Wt$ signal is then separated from the $t\bar{ t}$ background using boosted decision tree discriminants in two regions. The cross-section is extracted by fitting templates to the data distributions, and is measured to be $94 \pm 10$ (stat.)$^{ +28}_{ -22}$ (syst.) $\pm 2$ (lumi.) pb. The measurement is in agreement with the Standard Model prediction of $\sigma_{ \mathrm{ theory}} = 71.7 \pm 1.8\,(\mathrm{ scale})\,\pm 3.4\,(\mathrm{ PDF})\,\mathrm{ pb}$.
Categories: hep-ex