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| CMS-PAS-SMP-24-014 | ||
| Observation of 4$ \ell\gamma $ and evidence of $ ZZ\gamma $ production in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 2025-05-21 | ||
| Abstract: The first measurement of the production cross section of four charged leptons and a photon in proton-proton collisions is presented. The analysis utilises data collected by the CMS experiment from 2016 to 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The observed (expected) significance for the observation of $ \mathrm{pp} \rightarrow 4\ell \gamma $ in a phase space with $ p_{\mathrm{T}}^\gamma > $ 20 GeV, $ |\eta^\gamma| < $ 2.4 and $ \Delta R(\ell,\gamma) > $ 0.5 is 5.1 (4.1) standard deviations. The measured and expected fiducial cross sections are (0.16 $ \pm $ 0.06) fb and (0.10 $ \pm $ 0.03) fb respectively. The 4$ \ell\gamma $ events, with the additional requirement that the invariant mass of any of the two lepton pairs and the photon is greater than 100 GeV, are also used to search for the production of the triboson process, $ \mathrm{pp} \rightarrow ZZ\gamma $, with fully leptonic decays of the $ Z $ bosons, leading to the first evidence for this process, with an observed (expected) significance of 3.7 (3.0) standard deviations. The measured and expected fiducial cross sections for $ \mathrm{pp} \rightarrow ZZ\gamma \rightarrow 4\ell \gamma $ are (0.06 $ \pm $ 0.03) fb and (0.0 4$ \pm $ 0.02) fb , respectively. Both results are in agreement with the standard model prediction within one standard deviation. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative tree level SM Feynman diagrams with four isolated leptons and a photon in the final state. |
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Figure 1-a:
Representative tree level SM Feynman diagrams with four isolated leptons and a photon in the final state. |
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Figure 1-b:
Representative tree level SM Feynman diagrams with four isolated leptons and a photon in the final state. |
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Figure 2:
Momentum (left) and pseudorapidity (right) of the leading photon passing the loose selection and failing the tight cut-based ID in the non-prompt photon application region with four tight leptons. |
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Figure 2-a:
Momentum (left) and pseudorapidity (right) of the leading photon passing the loose selection and failing the tight cut-based ID in the non-prompt photon application region with four tight leptons. |
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Figure 2-b:
Momentum (left) and pseudorapidity (right) of the leading photon passing the loose selection and failing the tight cut-based ID in the non-prompt photon application region with four tight leptons. |
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Figure 3:
DataMC{mass of the $ \mathrm{Z}\mathrm{Z}\gamma $ system}{inclusive $ \mathrm{p}\mathrm{p}\to4\mathrm{l}\gamma $ cut-basedd |
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Figure 4:
DataMC{mass of the $ \mathrm{Z}\mathrm{Z}\gamma $ system}{triboson $ \mathrm{Z}\mathrm{Z}\gamma $ MVAs |
| Tables | |
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Table 1:
Sources of systematic uncertainty and their impact on the cross section measurement for the inclusive $ \mathrm{p}\mathrm{p}\to4\mathrm{l}\gamma $ final state and for the triboson $ \mathrm{Z}\mathrm{Z}\gamma $ final state. |
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Table 2:
Post-fit yields in the inclusive 4$ \mathrm{l}\gamma $ region. The uncertainties shown are the statistical uncertainties from the simulated samples and the data-driven non-prompt photons background. The row labelled '$ \mathrm{p}\mathrm{p}\to4\mathrm{l}\gamma $ OOA (out-of-acceptance)' indicates the number of events in the signal sample that fail the fiducial selection. |
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Table 3:
Post-fit yields in the triboson $ \mathrm{Z}\mathrm{Z}\gamma $ region. The uncertainties shown are the statistical uncertainties from the simulated samples and the data-driven non-prompt leptons background. The row labelled '$ \mathrm{Z}\mathrm{Z}\gamma\to4\mathrm{l}\gamma $ OOA (out-of-acceptance)' indicates the number of events in the signal sample that fail the fiducial selection. |
| Summary |
| The production cross section of the process $ \mathrm{p}\mathrm{p} \to 4 \mathrm{l}\gamma $, where the four leptons are either 4e, 2$ \mathrm{e} 2\mu $ or 4$ \mu $, is measured in a fiducial region in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data sample corresponds to an integrated luminosity of 138 fb$^{-1}$, collected with the CMS detector between 2016 and 2018. This study reports the first observation of the process, with a measured (expected) significance of 5.1 (4.1) standard deviations. The fiducial cross section of this process is measured and compared to the standard model prediction. Agreement is found between the two. The production of two Z bosons and a photon is searched for in a subset of the same region, with an additional selection aimed at excluding FSR contributions. The first evidence for the triboson production $ \mathrm{p}\mathrm{p} \to \mathrm{Z}\mathrm{Z}\gamma $, with the two Z bosons decaying leptonically to a pair of electrons or muons, is found with an observed (expected) significance of 3.7 (3.0) standard deviations. A good agreement between the measured cross section of this process and the standard model prediction is found. |
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