Aad, G.Abbott, B.Abbott, D.C.Abed Abud, A.Abeling, K.Abhayasinghe, D.K.Çetin, Serkant Ali2024-07-182024-07-1820220031-9007https://doi.org/10.1103/PhysRevLett.129.061803https://hdl.handle.net/11411/6374This Letter reports the observation of WWW production and a measurement of its cross section using 139 fb-1 of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWW production cross section is measured to be 820±100 (stat)±80 (syst) fb, approximately 2.6 standard deviations from the predicted cross section of 511±18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy. © 2022 CERN.eninfo:eu-repo/semantics/openAccessElementary ParticlesStatisticsA-CenterAtlas DetectorsCenter-Of-Mass EnergiesCentre-Of-Mass EnergiesCharged LeptonsLarge Hadron ColliderLarge-Hadron CollidersMeasurements OfProton Proton CollisionsStandard DeviationTellurium CompoundsArticleElectronExpectationHadronHumanLeptonArticle2-s2.0-8513651643710.1103/PhysRevLett.129.061803636018638Q1129