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
This Letter presents the observation and 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 √ s = 13 TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector ﬁducial phase-space region, deﬁned by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity diﬀerence. A total of 122 candidate events are observed for a background expectation of 69 ± 7 events, corresponding to an observed signal signiﬁcance of 6.5 standard deviations. The measured ﬁducial signal cross section is σ ﬁd. = 2 . 89 + 0 . 51 − 0 . 48 (stat.) + 0 . 29 − 0 . 28 (syst.) fb.