Evidence of ZZ gamma production and observation of 4 l gamma in proton-proton collisions at sqrt(s) = 13 TeV

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. Evidence for the process pp → ZZγ → 4lγ (l ¼ e, μ), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by pγT > 20 GeV, jηγ j < 2.4, ΔRðl; γÞ > 0.5, mZ between 60 and 120 GeV, and the invariant mass of either of the two Z bosons combined with the photon (mZγ) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is 60þ27−22 ab (47.56 0.04 ab). Additionally, the inclusive production of pp → 4lγ is studied by removing the mZγ requirement to include final state radiation where one Z boson decays to 2lγ, yielding an observed (expected) significance of 5.0 (4.2) standard deviations and a measured (predicted) fiducial cross section of 156þ39 −35 ab (99.97 0.09 ab).