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| CMS-PAS-HIG-18-018 | ||
| Measurement of the associated production of a Higgs boson and a pair of top-antitop quarks with the Higgs boson decaying to two photons in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| November 2018 | ||
| Abstract: This document reports the measurement of the rate of the associated production of a Higgs boson and a pair of top-antitop quarks ($\mathrm{t\bar{t}H}$), with the Higgs boson decaying into a pair of photons. Events with two photons are selected from a sample of proton-proton collisions at a center-of-mass energy $\sqrt{s}= $ 13 TeV collected by the CMS detector at the LHC in 2017, corresponding to an integrated luminosity of 41.5 fb$^{-1}$. The $\mathrm{t\bar{t}H}$ production is identified by requiring the presence of top quark decay products in the final state. The measured cross section, normalized to the standard model prediction, is 1.3$^{+0.7}_{-0.5}$. The combination with the published result using 35.9 fb$^{-1}$ of data recorded in 2016 at a center-of-mass energy $\sqrt{s}= $ 13 TeV is also reported. The combined best fit cross section, normalized to the standard model prediction, is found to be 1.7$^{+0.6}_{-0.5}$. All results are found in agreement with the standard model expectation. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Comparison of the dielectron invariant mass spectra in data and simulation, after applying energy scale corrections to data and energy smearing to the simulation, for $ {\mathrm {Z}} \to {{\mathrm {e}^+} {\mathrm {e}^-}} $ events with electrons reconstructed as photons. The comparison is shown for events with both electrons in the ECAL barrel (left) and for all the remaining events (right). Electrons are required to satisfy $ {R_\mathrm {9}} > $ 0.94. |
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Figure 1-a:
Comparison of the dielectron invariant mass spectra in data and simulation, after applying energy scale corrections to data and energy smearing to the simulation, for $ {\mathrm {Z}} \to {{\mathrm {e}^+} {\mathrm {e}^-}} $ events with electrons reconstructed as photons. The comparison is shown for events with both electrons in the ECAL barrel. |
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Figure 1-b:
Comparison of the dielectron invariant mass spectra in data and simulation, after applying energy scale corrections to data and energy smearing to the simulation, for $ {\mathrm {Z}} \to {{\mathrm {e}^+} {\mathrm {e}^-}} $ events with electrons reconstructed as photons. The comparison is shown for events with at least one electron not in the ECAL barrel. Electrons are required to satisfy $ {R_\mathrm {9}} > $ 0.94. |
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Figure 2:
Photon identification BDT score for $ {\mathrm {Z}} \to {{\mathrm {e}^+} {\mathrm {e}^-}} $ events in data and simulation, where the electrons are reconstructed as photons. Data (black markers) are compared to the Drell-Yan simulation (full histogram). The systematic uncertainty in the BDT output is shown in red. |
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Figure 3:
Distribution of the output of the $\mathrm{t\bar{t}H}$ BDTs for the leptonic categories (left) and the hadronic ones (right). Events are selected if the two photons have a photon identification score $ > -0.2$. At least one lepton and one b-tagged jet are required in the leptonic channel and no leptons and at least two jets in the hadronic one. Signal (red histogram) is compared to data sidebands (black markers), i.e. events in 100 $\leq \text {m}_{\gamma \gamma} < $ 115 GeV or 135 $\leq \text {m}_{\gamma \gamma} < $ 180 GeV, excluding the Higgs boson region. The signal histogram is scaled to match the area of the data one. Vertical lines represent the boundaries of the categories exploited in the analysis. |
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Figure 3-a:
Distribution of the output of the $\mathrm{t\bar{t}H}$ BDTs for the leptonic categories. Events are selected if the two photons have a photon identification score $ > -0.2$. At least one lepton and one b-tagged jet are required in the leptonic channel and no leptons and at least two jets in the hadronic one. Signal (red histogram) is compared to data sidebands (black markers), i.e. events in 100 $\leq \text {m}_{\gamma \gamma} < $ 115 GeV or 135 $\leq \text {m}_{\gamma \gamma} < $ 180 GeV, excluding the Higgs boson region. The signal histogram is scaled to match the area of the data one. Vertical lines represent the boundaries of the categories exploited in the analysis. |
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Figure 3-b:
Distribution of the output of the $\mathrm{t\bar{t}H}$ BDTs for the hadronic categories. Events are selected if the two photons have a photon identification score $ > -0.2$. At least one lepton and one b-tagged jet are required in the leptonic channel and no leptons and at least two jets in the hadronic one. Signal (red histogram) is compared to data sidebands (black markers), i.e. events in 100 $\leq \text {m}_{\gamma \gamma} < $ 115 GeV or 135 $\leq \text {m}_{\gamma \gamma} < $ 180 GeV, excluding the Higgs boson region. The signal histogram is scaled to match the area of the data one. Vertical lines represent the boundaries of the categories exploited in the analysis. |
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Figure 4:
Parametrized signal shape for all categories, weighted by S/(S+B) as defined in the text. The open squares represent weighted simulation events and the blue line the corresponding model. Also shown is the $\sigma _{\text {eff}}$ value (half the width of the narrowest interval containing 68.3% of the invariant mass distribution), the full width at half of the maximum (FWHM) and the corresponding interval. |
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Figure 5:
Expected fraction of signal events per production mode in the different categories. For each category, the $\sigma _{eff}$ and FWHM of the signal model, as described in the text, are given. The ratio of the number of signal events (S) to the number of signal plus background events (S+B) is shown on the right hand side. |
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Figure 6:
Data points (black) and signal plus background model fits in each category are shown. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-a:
Data points (black) and signal plus background model fit in the ttH Hadronic 0 category. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-b:
Data points (black) and signal plus background model fit in the ttH Hadronic 1 category. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-c:
Data points (black) and signal plus background model fit in the ttH Hadronic 2 category. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-d:
Data points (black) and signal plus background model fit in the ttH Leptonic 0 category. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-e:
Data points (black) and signal plus background model fit in the ttH Leptonic 1 category. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 6-f:
Data points (black) and signal plus background model fit for all categories, weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively. The $\mathrm{t\bar{t}H}$ signal strength reported in each plot is from the simultaneous fit to all 2017 categories. In the sum of all categories (bottom right), each category is weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
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Figure 7:
The likelihood scan for the $\mathrm{t\bar{t}H}$ signal strength where the value of the standard model Higgs boson mass is constrained to the Run I combination [9]. |
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Figure 8:
Signal strength modifiers measured for each analysis category (black points), with the value of the standard model Higgs boson mass constrained to the Run I combination, compared to the overall signal strength (green band) and to the SM expectation (dashed red line). |
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Figure 9:
The likelihood scan for the $\mathrm{t\bar{t}H}$ signal strength where the value of the SM Higgs boson mass is constrained to the Run I combination [9] in the fit combining 2016 and 2017 analysis. |
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Figure 10:
Data points (black) and signal plus background model fits for all categories weighted by S/(S + B), where S and B are the numbers of expected signal and background events, respectively, in a $ \pm $1$ \sigma _{eff}$ mass window centered on $m_{\textrm {H}}$. The $\mathrm{t\bar{t}H}$ signal strength (top left) is from a simultaneous fit to all categories. The one standard deviation (green) and two standard deviation (yellow) bands include the uncertainties in the background component of the fit. The solid red line shows the contribution from the total signal, plus the background contribution. The dashed red line shows the contribution from the background component of the fit. The bottom plot shows the residuals after subtraction of this background component. |
| Tables | |
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Table 1:
Schema of the photon preselection requirements. |
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Table 2:
The expected number of signal events per category and the percentage breakdown per production mode in that category. The $\sigma _{eff}$, computed as the smallest interval containing 68.3% of the invariant mass distribution, and FWHM, computed as the width of the distribution at half of its highest point divided by 2.35 are also shown as an estimate of the $m_{\gamma \gamma}$ resolution in that category. The expected number of background events per $ GeV $ around $125 GeV $ is also listed. |
| Summary |
| This paper reports the measurement of the $\mathrm{t\bar{t}H}$ production rate, with the Higgs boson decaying into a pair of photons. The analysis is based on 41.5 fb$^{-1}$ collected in 2017 by the CMS detector. The measured signal strength is $\mu = $ 1.3$^{+0.7}_{-0.5}$, corresponding to a significance relative to the background-only hypothesis of 3.1$\sigma$. The measurement is limited by the statistical uncertainty and is in agreement with the SM expectation. The combination with the corresponding 2016 data analysis [16] is also reported. The combined measured signal strength is $\mu = $ 1.7$^{+0.6}_{-0.5}$, corresponding to a significance relative to the background-only hypothesis of 4.1$\sigma$. |
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