CMS collaboration (2207 authors)Hollar, JonathanNayak, ArunaCalpas, BettyBargassa, PedrameBeirão Da Cruz E Silva, CristóvãoFaccioli, PietroFerreira Parracho, Pedro GuilhermeGallinaro, MicheleNguyen, FedericoRodrigues Antunes, JoaoSeixas, JoaoVarela, JoaoVischia, PietroLloret Iglesias, LaraDavid Tinoco Mendes, AndreMusella, PasqualeSilva, PedroPela, JoaoLeonardo, Nuno2019-02-042019-02-042014-06-09http://dx.doi.org/10.1103/PhysRevLett.112.231802http://hdl.handle.net/10400.26/26526The first observation of the associated production of a single top quark and a W boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of 12.2 inverse femtobarns of proton-proton collisions at sqrt(s) = 8 TeV recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a b quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant t t-bar background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is 23.4 +- 5.4 pb, in agreement with the standard model prediction.engjournal article2019-02-04