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

CMS Collaboration

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$γ$ $\to$ 4$\ellγ$ ($\ell$ = e, $μ$), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by $p_\mathrm{T}^γ$ $\gt$ 20 GeV, $\lvertη^γ\rvert$ $\lt$ 2.4, $ΔR(\ell,γ)$ $\gt$ 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 ($m_{\text{Z}γ}$) 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$\ellγ$ is studied by removing the $m_{\text{Z}γ}$ requirement to include final state radiation where one Z boson decays to 2$\ellγ$, 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).

Evidence of ZZ$γ$ production and observation of $4\ellγ$ 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. The first evidence for the process pp ZZ 4 ( = e, ), with an observed (expected) significance of 3.7 (3.1) standard deviations in a fiducial region defined by 20 GeV, 2.4, 0.5, between 60 and 120 GeV, and the invariant mass of either of the two Z bosons combined with the photon () larger than 100 GeV, is reported. The measured (predicted) fiducial cross section is 60 ab (47.56 0.04 ab). Additionally, the inclusive production of pp 4 is studied by removing the requirement to include final state radiation where one Z boson decays to 2, yielding an observed (expected) significance of 5.0 (4.2) standard deviations and a measured (predicted) fiducial cross section of 156 ab (99.97 0.09 ab).

Paper Structure

This paper contains 1 section, 3 figures, 1 table.

Table of Contents

  1. The CMS Collaboration

Figures (3)

  • Figure 1: Representative tree-level standard model Feynman diagrams with four isolated leptons and a photon in the final state. From left to right, photon emitted from a quark line, associated ${ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ production, and final-state radiation.
  • Figure 2: Transverse momentum (upper) and pseudorapidity (lower) of the leading photon passing the loose selection and failing the tight cutoff-based identification in the nonprompt photon application region with four tight leptons. The vertical bars represent the statistical uncertainties in the data. The hatched area represents the statistical uncertainties in the simulation.
  • Figure 3: Post-fit mass distributions of the ${ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace$ system in the triboson ${ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace$ (upper) and inclusive ${ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace\to4{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upgamma}}{} _{ {}} ^{ {}}} }\xspace$ (lower) regions, obtained with the cutoff-based and multivariate photon identification, respectively. The last bin includes the events exceeding the upper bound of the x-axis. The vertical bars represent the statistical uncertainties in the data. The hatched area represents the statistical uncertainties in the simulation.