CMS-HIG-21-015

CMS-HIG-21-015 ; CERN-EP-2022-131
Search for the Higgs boson decay to a pair of electrons in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
30 July 2022
Phys. Lett. B 846 (2023) 137783
Abstract: A search is presented for the Higgs boson decay to a pair of electrons (e$^{+}$e$^{-}$) in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The data set was collected with the CMS experiment at the LHC between 2016 and 2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis uses event categories targeting Higgs boson production via gluon fusion and vector boson fusion. The observed upper limit on the Higgs boson branching fraction to an electron pair is 3.0 $\times$ 10$^{-4}$ (3.0 $\times$ 10$^{-4}$ expected) at the 95% confidence level, which is the most stringent limit on this branching fraction to date.
Links: e-print arXiv:2208.00265 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distribution of the output score of the VBF BDT in all simulated background and signal events, and data (left), passing VBF preselection. The ggH and VBF signals are scaled for better visibility. Category boundaries targeting VBF production are denoted with dashed lines. The shaded region defines events which are not selected to enter VBF analysis categories, but may populate those targeting ggH. The right plot shows the distribution of the output score of the VBF BDT in a control region around the Z boson mass. The combined impact of the statistical and systematic uncertainties in simulation is shown by the red shaded band, where the systematic component includes uncertainties on the jet energy scale and resolution corrections, alongside the electron energy scale corrections. Uncertainties in the efficiency of electron identification, reconstruction, and trigger selection are also included, as well as the uncertainty on the integrated luminosity, presented in Section 7. Good agreement is observed between the DY simulation (filled histogram) and data (black markers), within the phase space in which the analysis categories are constructed.
png pdf	Figure 1-a: Distribution of the output score of the VBF BDT in all simulated background and signal events, and data, passing VBF preselection. The ggH and VBF signals are scaled for better visibility. Category boundaries targeting VBF production are denoted with dashed lines. The shaded region defines events which are not selected to enter VBF analysis categories, but may populate those targeting ggH. The combined impact of the statistical and systematic uncertainties in simulation is shown by the red shaded band, where the systematic component includes uncertainties on the jet energy scale and resolution corrections, alongside the electron energy scale corrections. Uncertainties in the efficiency of electron identification, reconstruction, and trigger selection are also included, as well as the uncertainty on the integrated luminosity, presented in Section 7.
png pdf	Figure 1-b: Distribution of the output score of the VBF BDT in a control region around the Z boson mass. The combined impact of the statistical and systematic uncertainties in simulation is shown by the red shaded band, where the systematic component includes uncertainties on the jet energy scale and resolution corrections, alongside the electron energy scale corrections. Uncertainties in the efficiency of electron identification, reconstruction, and trigger selection are also included, as well as the uncertainty on the integrated luminosity, presented in Section 7. Good agreement is observed between the DY simulation (filled histogram) and data (black markers), within the phase space in which the analysis categories are constructed.
png pdf	Figure 2: Distribution of the output score of the ggH BDT in simulated background and signal events, and data (left). The ggH and VBF signals are scaled such that they are visible. Category boundaries targeting ggH Higgs boson production are denoted with dashed lines. Events with scores in the grey shaded region are discarded from the analysis. The right plot shows the distribution of the output score of the ggH BDT in a control region around the Z boson mass. Agreement is compared between the DY simulation (filled histogram) and data (black points). The combined impact of the statistical and systematic uncertainties in simulation is shown by the red shaded band, where the sources contributing to the systematic component are identical to those included in Fig. 1. Residual differences between data and simulation are smaller than the ggH cross section uncertainty which is included in the final maximum likelihood fit.
png pdf	Figure 2-a: Distribution of the output score of the ggH BDT in simulated background and signal events, and data. The ggH and VBF signals are scaled such that they are visible. Category boundaries targeting ggH Higgs boson production are denoted with dashed lines. Events with scores in the grey shaded region are discarded from the analysis.
png pdf	Figure 2-b: Distribution of the output score of the ggH BDT in a control region around the Z boson mass. Agreement is compared between the DY simulation (filled histogram) and data (black points). The combined impact of the statistical and systematic uncertainties in simulation is shown by the red shaded band, where the sources contributing to the systematic component are identical to those included in Fig. 1. Residual differences between data and simulation are smaller than the ggH cross section uncertainty which is included in the final maximum likelihood fit.
png pdf	Figure 3: Signal models for the highest S/B categories targeting ggH and VBF processes, integrated over production processes, for Higgs boson events simulated at $ {m_\mathrm{H}} = $ 125 GeV. Contributions from each of the three years are shown by the dashed lines. The models are normalized to unit area. The ${\sigma _{\text {eff}}}$ is the smallest interval containing 68.3% of the ${m_{\mathrm{e} \mathrm{e}}}$ signal distribution.
png pdf	Figure 3-a: Signal models for the highest S/B category targeting the VBF process, integrated over production processes, for Higgs boson events simulated at $ {m_\mathrm{H}} = $ 125 GeV. Contributions from each of the three years are shown by the dashed lines. The models are normalized to unit area. The ${\sigma _{\text {eff}}}$ is the smallest interval containing 68.3% of the ${m_{\mathrm{e} \mathrm{e}}}$ signal distribution.
png pdf	Figure 3-b: Signal models for the highest S/B categories targeting ggH and VBF processes, integrated over production processes, for Higgs boson events simulated at $ {m_\mathrm{H}} = $ 125 GeV. Contributions from each of the three years are shown by the dashed lines. The models are normalized to unit area. The ${\sigma _{\text {eff}}}$ is the smallest interval containing 68.3% of the ${m_{\mathrm{e} \mathrm{e}}}$ signal distribution.
png pdf	Figure 4: The signal-plus-background model fit to the ${m_{\mathrm{e} \mathrm{e}}}$ distribution for the highest S/B analysis categories targeting the ggH (left) and VBF (right) processes. The signal model for each category is also shown, scaled to the observed limit at $ {m_\mathrm{H}} = $ 125.38 GeV. The one (green) and two (yellow) standard deviation bands show the uncertainties in the background component of the fit. The lower panel shows the residuals after subtraction of this background component. The background functions describe the data well, with no excess observed.
png pdf	Figure 4-a: The signal-plus-background model fit to the ${m_{\mathrm{e} \mathrm{e}}}$ distribution for the highest S/B analysis categories targeting the ggH process. The signal model is also shown, scaled to the observed limit at $ {m_\mathrm{H}} = $ 125.38 GeV. The one (green) and two (yellow) standard deviation bands show the uncertainties in the background component of the fit. The lower panel shows the residuals after subtraction of this background component. The background functions describe the data well, with no excess observed.
png pdf	Figure 4-b: The signal-plus-background model fit to the ${m_{\mathrm{e} \mathrm{e}}}$ distribution for the highest S/B analysis categories targeting the VBF process. The signal model is also shown, scaled to the observed limit at $ {m_\mathrm{H}} = $ 125.38 GeV. The one (green) and two (yellow) standard deviation bands show the uncertainties in the background component of the fit. The lower panel shows the residuals after subtraction of this background component. The background functions describe the data well, with no excess observed.
png pdf	Figure 5: Expected and observed limits on ${\mathcal {B}({\mathrm{H} \to \mathrm{e^{+}} \mathrm{e^{-}}})}$ for a Higgs boson mass between 120-130 GeV.
png pdf	Figure 6: Expected and observed limits on ${\mathcal {B}({\mathrm{H} \to \mathrm{e^{+}} \mathrm{e^{-}}})}$ for each analysis category, and all categories combined The results here are computed for $ {m_\mathrm{H}} = $ 125.38 GeV.

Tables

png pdf

Table 1:
The total expected number of signal events for $ {m_\mathrm{H}} = $ 125.38 GeV in analysis categories targeting ggH and VBF events, for an integrated luminosity of 138 fb$^{-1}$. The fractional contribution from each production mode to each category is also shown. The ${\sigma _{\text {eff}}}$, defined as the smallest interval containing 68.3% of the ${m_{\mathrm{e} \mathrm{e}}}$ distribution, is listed for each analysis category. The final column shows the expected ratio of signal to background, where S and B are the numbers of expected signal and background events in a $ \pm $1$ {\sigma _{\text {eff}}} $ window centred on $m_\mathrm{H}$.

Summary

A search for the Higgs boson decaying to an e$^{+}$e$^{-}$ pair is performed using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV with the CMS experiment at the LHC between 2016-2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis uses categories targeting Higgs boson production via gluon fusion and vector boson fusion, with dedicated boosted decision tree classifiers trained for each production mode to enhance the sensitivity of the resulting categories. A maximum likelihood fit to the dielectron mass distribution is performed simultaneously in each analysis category to extract an upper limit on the Higgs boson to electron pair branching fraction; the resulting observed (expected) limit at the 95% confidence level on the branching fraction for H $\to$ e$^{+}$e$^{-}$ decays is 3.0 $ \times$ 10$^{-4} $ (3.0 $ \times$ 10$^{-4} $). This is the most stringent limit on the Higgs boson branching fraction to an e$^{+}$e$^{-}$ pair to date. When compared with the previous best limit from the CMS Collaboration [18], where analysis categories were constructed using a selection on electron and jet kinematics, the improvement in sensitivity presented in this Letter is attributed primarily to the use of BDT classifiers, which significantly improve the S/B ratio of analysis categories. Accounting both for the increase in integrated luminosity and centre-of-mass energy, the use of BDT classifiers further improves the limit on $ \mathcal{B}(\mathrm{H}\to\mathrm{e}^+\mathrm{e}^-) $ by a factor of approximately 1.5.

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