Evidence 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 𝑝𝛾T>20 GeV, |𝜂𝛾|<2.4, Δ⁢𝑅⁢(ℓ,𝛾)>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 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