CMSHIG17007 ; CERNEP2018092  
Search for the decay of a Higgs boson in the $\ell\ell\gamma$ channel in protonproton collisions at $\sqrt{s} = $ 13 TeV  
CMS Collaboration  
15 June 2018  
JHEP 11 (2018) 152  
Abstract: A search for a Higgs boson decaying into a pair of electrons or muons and a photon is described. Higgs boson decays to a Z boson and a photon ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$,$\ell=\mathrm{e}$ or $\mu$), or to two photons, one of which has an internal conversion into a muon pair ($\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$) were considered. The analysis is performed using a data set recorded by the CMS experiment at the LHC from protonproton collisions at a centerofmass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{1}$. No significant excess above the background prediction has been found. Limits are set on the cross section for a standard model Higgs boson decaying to oppositesign electron or muon pairs and a photon. The observed limits on cross section times the corresponding branching fractions vary between 1.4 and 4.0 (6.1 and 11.4) times the standard model cross section for $\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$ ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$) in the 120130 GeV mass range of the $\ell\ell\gamma$ system. The $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ and $\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$ analyses are combined for $m_\mathrm{H} = $ 125 GeV, obtaining an observed (expected) 95% confidence level upper limit of 3.9 (2.0) times the standard model cross section.  
Links: eprint arXiv:1806.05996 [hepex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; 
Figures  
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Figure 1:
Dominant Feynman diagrams contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1a:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1b:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1c:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1d:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1e:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1f:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 1g:
One of the dominant Feynman diagram contributing to the $ {\mathrm {H}} \to \ell \ell \gamma $ process. 
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Figure 2:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EBhigh $ {R_\mathrm {9}}$ (upper left), EBlow $ {R_\mathrm {9}}$ (upper right), EE (lower left) and dijet tag (lower right) for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 2a:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EBhigh $ {R_\mathrm {9}}$ for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 2b:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EBlow $ {R_\mathrm {9}}$ for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 2c:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for EE for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 2d:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for dijet tag (upper left), boosted (upper right), untagged 1 (middle left), untagged 2 (middle right), untagged 3 (bottom left), and untagged 4 (bottom right) for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3a:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3b:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for boosted for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3c:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 1 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3d:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 2 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3e:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 3 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 3f:
Background model fit to the $m_{{\mathrm {e}} {\mathrm {e}}\gamma}$ distribution for untagged 4 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to {\mathrm {e}} {\mathrm {e}}\gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 4:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag (upper left), boosted (upper right), untagged 1 (middle left), untagged 2 (middle right), untagged 3 (bottom left), and untagged 4 (bottom right) for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 4a:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 4b:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for boosted for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 4c:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 1 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
png pdf 
Figure 4d:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 2 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
png pdf 
Figure 4e:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 3 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
png pdf 
Figure 4f:
Background model fit to the $m_{\mu \mu \gamma}$ distribution for dijet tag boosted untagged 4 for the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \mu \mu \gamma $ selection. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 5:
Background model fit to the $m_{\ell \ell \gamma}$ distribution for $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ lepton tag category. The green and yellow bands represent the 68 and 95% CL uncertainties in the fit to the data. 
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Figure 6:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ process (upper plot) and the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ process (lower plot) relative to the SM prediction, as a function of the Higgs boson mass. 
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Figure 6a:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ process relative to the SM prediction, as a function of the Higgs boson mass. 
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Figure 6b:
Exclusion limit, at 95% CL, on the cross section of the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ process relative to the SM prediction, as a function of the Higgs boson mass. 
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Figure 7:
Exclusion limit, at 95% CL, on the cross section of $ {\mathrm {H}} \to \ell \ell \gamma $ relative to the SM prediction, for an SM Higgs boson of $m_ {\mathrm {H}} = $ 125 GeV. The upper limits of each analysis category, as well as their combinations, are shown. Black full (empty) circles show the observed (background only expected) limit. Red circles show the expected upper limit assuming an SM Higgs boson decaying to $\ell \ell \gamma $ decay channel. 
Tables  
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Table 1:
Categories in $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ search. The electron and muon channels are considered separately in all classes except for the leptontag class. 
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Table 2:
Expected signal yields for a 125 GeV SM Higgs boson, corresponding to an integrated luminosity of 35.9 fb$^{1}$, for all categories in the $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ and $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ processes in the narrowest $\ell \ell \gamma $ invariant mass window around 125 GeV containing 68.3% of the expected signal distribution. 
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Table 3:
Fit functions chosen as a result of the bias study used in the analysis. 
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Table 4:
Sources of systematic uncertainties considered in the $ {\mathrm {H}} \to {\mathrm {Z}}\gamma \to \ell \ell \gamma $ and $ {\mathrm {H}} \to \gamma ^*\gamma \to \mu \mu \gamma $ analyses. The prefit values of the nuisance parameters are shown averaged over all the categories in the analysis which either affect the normalization of the simulated signal event yields or the mean and resolution of $m_{\ell \ell \gamma}$. The "'' indicates that the uncertainty is not applicable. 
Summary 
A search is performed for a standard model (SM) Higgs boson decaying into a lepton pair and a photon. This final state has contributions from Higgs boson decays to a Z boson and a photon ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$,$\ell=\mathrm{e}$ or $\mu$), or to two photons, one of which has an internal conversion into a muon pair ($\mathrm{H}\to\gamma^{*}\gamma\to\mu\mu\gamma$). The analysis is performed using a data set from pp collisions at a centerofmass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{1}$. No significant excess above the expected background is found. Limits on the Higgs boson production cross section times the corresponding branching fractions are set. The expected exclusion limits at 95% confidence level are about 2.12.3 (3.99.1) times the SM cross section in the $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ ($\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$) channel in the mass range from 120 to 130 GeV, and the observed limit varies between about 1.4 and 4.0 (6.1 and 11.4) times the SM cross section. Finally, the $\mathrm{H}\to\gamma^*\gamma\to\mu\mu\gamma$ and $\mathrm{H}\to\mathrm{Z}\gamma\to\ell\ell\gamma$ analyses are combined for $m_\mathrm{H} = $ 125 GeV, obtaining an observed (expected) 95% confidence level upper limit of 3.9 (2.0) times the SM cross section. 
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