The inclusive cross section for the production of a single top quark in association with a π boson is measured using 140ββfbβ1 of proton-proton collision data collected with the ATLAS detector at βπ =13ββTeV. Events containing two charged leptons and at least one jet identified as originating from a π-quark are selected. A multivariate discriminant is constructed to separate the π‘β’π signal from the π‘β’
Β―
π‘
background. The cross section is extracted using a profile likelihood fit to the signal and control regions and it is measured to be ππ‘β’π=7β’5+15
β14ββpb, 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 πβ’π‘β’π vertex times the Cabibbo-Kobayashi-Maskawa matrix element |πLVβ’ππ‘β’π| of 0.97Β±0.10.
