ATLAS, CollaborationCollaborationATLASAgustoni, MarcoMarcoAgustoniBeck, Hans PeterHans PeterBeck0000-0001-7212-1096Cervelli, AlbertoAlbertoCervelliEreditato, AntonioAntonioEreditatoHaug, SigveSigveHaug0000-0003-0442-3361Kabana, SonjaSonjaKabanaMarti, LukasLukasMartiMeloni, FedericoFedericoMeloniPretzl, Klaus-PeterKlaus-PeterPretzlSchneider, BasilBasilSchneiderStramaglia, Maria ElenaMaria ElenaStramagliaStucci, StefaniaStefaniaStucciWeber, MichaelMichaelWeber0000-0002-2770-90312024-10-242024-10-242015https://boris-portal.unibe.ch/handle/20.500.12422/144632This 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 σ s =5.0± 4.3 pb, consistent with the Standard Model expectation.en500 - Science::530 - Physicsarticle10.7892/boris.876861410.064710.1016/j.physletb.2014.11.042