Measurement of single top-quark production in association with a W boson in pp collisions at √s = 13 TeV with the ATLAS detector

The inclusive cross section for the production of a single top quark in association with a 𝑊 boson is measured using 140  fb⁻¹ of proton-proton collision data collected with the ATLAS detector at √𝑠 = 13  TeV. Events containing two charged leptons and at least one jet identified as originating from a 𝑏-quark are selected. A multivariate discriminant is constructed to separate the 𝑡⁢𝑊 signal from the 𝑡⁢𝑡¯
background. The cross section is extracted using a profile likelihood fit to the signal and control regions and it is measured to be 𝜎_𝑡⁢𝑊  = 7⁢5⁺¹⁵₋₁₄  pb, in good agreement with the Standard Model prediction. The measured cross section is used to extract a value for the left-handed form factor at the 𝑊⁢𝑡⁢𝑏 vertex times the Cabibbo-Kobayashi-Maskawa matrix element |𝑓_LV⁡𝑉_𝑡⁢𝑏| of 0.97 ±0.10.