Observation of electroweak production of a same-sign W boson pair in association with two jets in pp collisions at sqrt(s)=13 TeV with the ATLAS detector

We present the observation and fiducial cross-section measurement of electroweak production of a same-sign W boson pair in association with two jets using 36.1 fb-1 of proton-proton collision data recorded at a center-of-mass energy of sqrt(s)=13 TeV by the ATLAS detector at the Large Hadron Collider. Events containing two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference, are selected. A total of 122 candidate events is observed for a background expectation of 69±10 events, giving an observed (expected) signal significance of 6.9 (4.6) standard deviations. The fiducial cross section for the electroweak production process is measured to be 2.91+0.51/-0.47(stat.)±0.27(sys.) fb.