Observation of Wγγ triboson production in proton-proton collisions at √s = 13 TeV with the ATLAS detector

This letter reports the observation of W(ιν)_ΥΥ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of √s = 13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb⁻¹. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(eν )_ΥΥ and W(μν)ΥΥ events is measured to be σ_fid = 13.8 ± 1.1 (stat) ^+2.1_-2.0 (syst) ± 0.1 (lumi) fb, in agreement with the Standard Model prediction.