Evidence of ZZ$\gamma$ production and observation of $4\ell\gamma$ in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports the first evidence of ZZγ production and observation of 4lγ in proton-proton collisions at 13 TeV using CMS data, with significance levels of 3.7 and 5.0 standard deviations respectively.

Contribution

It provides the first evidence for pp → ZZγ → 4lγ and measures the fiducial cross sections, advancing understanding of multi-boson production at high energies.

Findings

Evidence of ZZγ production with 3.7σ significance.

Observation of 4lγ production with 5.0σ significance.

Measured fiducial cross sections consistent with predictions.

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$^{-1}$. The first evidence for the process pp $\to$ ZZ$\gamma$ $\to$ 4$\ell\gamma$ ($\ell$ = e, $\mu$), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by $p_\mathrm{T}^\gamma$ $\gt$ 20 GeV, $\lvert\eta^\gamma\rvert$ $\lt$ 2.4, $\Delta R(\ell,\gamma)$ $\gt$ 0.5, $m_\text{Z}$ between 60 and 120 GeV, and the invariant mass of either of the two Z bosons combined with the photon ($m_{\text{Z}\gamma}$) larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is 60$^{+27}_{-22}$ ab (47.56 $\pm$ 0.04 ab). Additionally, the inclusive production of pp $\to$ 4$\ell\gamma$ is studied by removing the $m_{\text{Z}\gamma}$ requirement to include final state radiation where one Z boson decays to 2$\ell\gamma$, 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 $\pm$ 0.09 ab).