Aad, G.Abbott, B.Abbott, D.C.Abed Abud, A.Abeling, K.Abhayasinghe, D.K.Abidi, S.H.AbouZeid, O.S.Abraham, N.L.Abramowicz, H.Albert, JustinAnelli, Christopher R.Chiu, Y. H.Ghasemi Bostanabad, M.Hamano, KenjiKay, E. F.Keeler, RichardKowalewski, RobertLefebvre, MichelMcLean, K.D.et al.2021-01-262021-01-2620202020Aad, G., Abbott, B., Abbott, D. C., Abed Abud, A., Abeling, K., Abhayasinghe, D. K., … Zwalinski, L. (2020). Observation of the associated production of a top quark and a Z boson in pp collisions at √s= 13 TeV with the ATLAS detector. Journal of High Energy Physics, 2020(7). https://doi.org/10.1007/JHEP07(2020)124https://doi.org/10.1007/JHEP07(2020)124http://hdl.handle.net/1828/12595Single top-quark production in association with a Z boson, where the Z boson decays to a pair of charged leptons, is measured in the trilepton channel. The proton-proton collision data collected by the ATLAS experiment from 2015 to 2018 at a centre-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 139 fb−1. Events containing three isolated charged leptons (electrons or muons) and two or three jets, one of which is identified as containing a b-hadron, are selected. The main backgrounds are from tt¯Z and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for tℓ+ℓ−q production, including non-resonant dilepton pairs with mℓ+ℓ− > 30 GeV, is 97 ± 13 (stat.) ± 7 (syst.) fb, consistent with the Standard Model prediction.enHadron-Hadron scattering (experiments)ArticleDepartment of Physics and Astronomy