Aad, G.Abbott, B.Abeling, K.Abicht, N.J.Abidi, S.H.Aboulhorma, A.Çetin, Serkant Ali2024-05-192024-05-1920240370-2693https://doi.org/10.1016/j.physletb.2023.138400https://hdl.handle.net/20.500.12713/4500This letter reports the observation of W(??)?? 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(e?)?? and W(??)?? 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. © 2023 The Author(s)eninfo:eu-repo/semantics/openAccessArticle8482-s2.0-8518421050410.1016/j.physletb.2023.138400Q1