This letter reports the observation of 𝑊 (𝓁𝜈)𝛾𝛾 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)𝛾𝛾 and 𝑊 (𝜇𝜈)𝛾𝛾 events is measured to be 𝜎fid = 13.8 ± 1.1(stat)+2.1 −2.0(syst) ± 0.1(lumi) fb, in agreement with the Standard Model prediction.

Aad, G., Abbott, B., Abeling, K., Abicht, N., Abidi, S., Aboulhorma, A., et al. (2024). Observation of 𝑊 𝛾𝛾 triboson production in proton-proton collisions at √𝑠 = 13 TeV with the ATLAS detector. PHYSICS LETTERS. SECTION B, 848, 1-24 [10.1016/j.physletb.2023.138400].

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

Alberghi, G. L.;Alfonsi, F.;Bindi, M.;Boscherini, D.;Cabras, G.;Carratta, G.;Cavalli, N.;De Castro, S.;Fabbri, F.;Fabbri, L.;Franchini, M.;Gabrielli, A.;Lasagni Manghi, F.;Massa, L.;Monzani, S.;