PT Journal AU ATLAS Collaboration (Aad, Gea Amos, KR Aparisi Pozo, JA Bailey, AJ Bouchhar, N Cabrera Urban, S Cantero, J Cardillo, F Castillo Gimenez, V Chitishvili, M Costa, MJ Didenko Escobar, C Fiorini, L Fullana Torregrosa, E Fuster, J Garcia, C Garcia Navarro, JE Gomez Delegido, AJ Gonzalez de la Hoz, S Gonzalvo Rodriguez, GR Guerrero Rojas, JGR Lacasta, C Marti-Garcia, S Martinez Agullo, P Miralles Lopez, M Mitsou, VA Monsonis Romero, L Moreno Llacer, M Munoz Perez, D Navarro-Gonzalez, J Poveda, J Prades Ibañez, A Rubio Jimenez, A Ruiz-Martinez, A Sabatini, P Salt, J Sanchez Sebastian, V Sayago Galvan, I Senthilkumar, V Soldevila, U Sanchez, J Torro Pastor, E Valero, A Valiente Moreno, E Valls Ferrer, JA Varriale, L Villaplana Perez, M Vos, M TI Observation of Wγγ triboson production in proton-proton collisions at √s=13 TeV with the ATLAS detector SO Physics Letters B JI Phys. Lett. B PY 2024 BP 138400 EP 24pp VL 848 DI 10.1016/j.physletb.2023.138400 LA English AB This letter reports the observation of () production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of root= 13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb-1. Events with a leptonically-decaying 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 () and () events is measured to be fid = 13.8 +/- 1.1(stat)+2.1-2.0(syst) +/- 0.1(lumi) fb, in agreement with the Standard Model prediction. ER