Evidence of of 𝑍⁢𝑍⁢𝛾 Production and Observation of 4⁢ℓ⁢𝛾 in Proton-Proton Collisions at √𝑠 = 13 TeV

Abstract

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 𝑝⁢𝑝 → 𝑍⁢𝑍⁢𝛾 → 4⁢ℓ⁢𝛾 (ℓ = 𝑒, 𝜇), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by 𝑝^𝛾_T > 20 GeV, |𝜂^𝛾| < 2.4, Δ⁢𝑅⁢(ℓ,𝛾) > 0.5, 𝑚_𝑍 between 60 and 120 GeV, and the invariant mass of either of the two 𝑍 bosons combined with the photon (𝑚_𝑍_𝛾) 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 𝑝⁢𝑝 → 4⁢ℓ⁢𝛾 is studied by removing the 𝑚𝑍𝛾 requirement to include final state radiation where one 𝑍 boson decays to 2⁢ℓ⁢𝛾, 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).