ATLAS collaboration (2889 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCantrill, RobertCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséOnofre, AntónioPalma, AlbertoPedro, RutePina, João AntonioPinto, BelmiroSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042014-11-19http://dx.doi.org/10.1016/j.physletb.2014.11.042http://hdl.handle.net/10400.26/26698This Letter presents a search at the LHC for s -channel single top-quark production in proton–proton collisions at a centre-of-mass energy of 8 TeV. The analyzed data set was recorded by the ATLAS detector and corresponds to an integrated luminosity of 20.3 fb −1 . Selected events contain one charged lepton, large missing transverse momentum and exactly two b -tagged jets. A multivariate event classifier based on boosted decision trees is developed to discriminate s -channel single top-quark events from the main background contributions. The signal extraction is based on a binned maximum-likelihood fit of the output classifier distribution. The analysis leads to an upper limit on the s -channel single top-quark production cross-section of 14.6 pb at the 95% confidence level. The fit gives a cross-section of σs=5.0±4.3 pb , consistent with the Standard Model expectation.engjournal article2019-02-04