Measurement of single top-quark production in the s-channel in proton−proton collisions at √s = 13 TeV with the ATLAS detector

A measurement of single top-quark production in the s-channel is performed in proton−proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The dataset corresponds to an integrated luminosity of 139 fb⁻¹. The analysis is performed on events with an electron or muon, missing transverse momentum and exactly two b-tagged jets in the final state. A discriminant based on matrix element calculations is used to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W-boson production in association with jets. The observed (expected) signal significance over the background-only hypothesis is 3.3 (3.9) standard deviations, and the measured cross-section is σ=8.2^+3.5_−2.9 pb, consistent with the Standard Model prediction of σ^SM=10.32^+0.40_−0.36 pb.