Observation of electroweak production of same-sign W boson pairs in the two jet and two same-sign lepton final state in proton-proton collisions at 13 TeV

The observation of electroweak production of same-sign W boson pairs in proton-proton collisions at $13~\mathrm{TeV}$ is reported. The data sample corresponds to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$ collected with the CMS detector. Events are selected by requiring exactly two leptons of the same charge, moderate missing momentum, and two jets with large rapidity separation and large dijet mass. The observed significance is 5.5 standard deviations, where a significance of 5.7 standard deviations is expected based on the standard model. A cross section measurement in a fiducial region is reported. Bounds on the structure of quartic vector-boson interactions are given in the framework of dimension-eight effective field theory operators, together with upper limits on the production of doubly charged Higgs bosons.