Evidence of ZZ$\gamma$ production and observation of $4\ell \gamma$ in proton-proton collisions at $\sqrt{s}$ = 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${}^{-1}$. 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 $p_{\mathrm{T}}^{\gamma }$ $>$ 20 GeV, $|{\eta }^{\gamma }|$ $<$ 2.4, $\Delta R(\ell ,\gamma )$ $>$ 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 ${}_{-22}^{+27}$ 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 ${}_{-35}^{+39}$ ab (99.97 $\pm$ 0.09 ab).

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/SMP-24-014 (CMS Public Pages)

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