Evidence of the production of two Z bosons and a photon in proton-proton collisions is reported for the first time in CMS. The analysis uses data collected by the CMS experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb^-1. The first evidence for the process pp ZZγ 4γ (= e, μ), with an observed (expected) significance of 3. 7 (3. 1) standard deviations in a fiducial region defined by pT^γ 20 GeV, η^γ 2. 4, ΔR (, γ) 0. 5, mZ between 60 and 120 GeV, and the invariant mass of either of the two Z bosons combined with the photon (mₙ⏒) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is 60^+27-₂₂ ab (47. 56 0. 04 ab). Additionally, the inclusive production of pp 4γ is studied by removing the mₙ⏒ requirement to include final state radiation where one Z boson decays to 2γ, yielding an observed (expected) significance of 5. 0 (4. 2) standard deviations and a measured (predicted) fiducial cross section of 156^+39-₃₅ ab (99. 97 0. 09 ab).
Hayrapetyan et al. (Thu,) studied this question.