First observation of W associated single top (tW) production in proton-proton collisions at 8 TeV

The first observation of the associated production of a single top quark and a W boson in proton-proton collisions at p s = 8 TeV with the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 12.2 fb-1. The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is used to separate the signal from the t ̄ t background. The signal is observed with a 6.0 standard deviation excess above a background only hypothesis. A production cross section of 23 : 4 + 5 : 5 pb is measured, in agreement with the standard model expectation of 22 : 2 1 : 5 pb