CMS-HIG-21-006 ; CERN-EP-2022-157 | ||
Search for CP violation in ttH and tH production in multilepton channels in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
4 August 2022 | ||
JHEP 07 (2023) 092 | ||
Abstract: The charge-parity (CP) structure of the Yukawa interaction between the Higgs (H) boson and the top quark is measured in a data sample enriched in the ttH and tH associated production, using 138 fb$^{-1}$ of data collected in proton-proton collisions at $\sqrt{s} = $ 13 TeV by the CMS experiment at the CERN LHC. The study targets events where the H boson decays via H $\to$ WW or H $\to\tau\tau$ and the top quarks decay via t $\to$ Wb: the W bosons decay either leptonically or hadronically, and final states characterized by the presence of at least two leptons are studied. Machine learning techniques are applied to these final states to enhance the separation of CP-even from CP-odd scenarios. Two-dimensional confidence regions are set on ${\kappa_{\mathrm{t}}}$ and ${\tilde{\kappa}_{\mathrm{t}}}$, which are respectively defined as the CP-even and CP-odd top-Higgs Yukawa coupling modifiers. No significant fractional CP-odd contributions, parameterized by the quantity ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|}$ are observed; the parameter is determined to be ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} =$ 0.59 with an interval of (0.24, 0.81) at 68% confidence level. The results are combined with previous results covering the H $\to$ ZZ and H $\to\gamma\gamma$ decay modes, yielding two- and one-dimensional confidence regions on ${\kappa_{\mathrm{t}}}$ and ${\tilde{\kappa}_{\mathrm{t}}}$, while ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|}$ is determined to be ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} =$ 0.28 with an interval of ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} <$ 0.55 at 68% confidence level, in agreement with the standard model CP-even prediction of ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} =$ 0. | ||
Links: e-print arXiv:2208.02686 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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Figures | |
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Figure 1:
Representative Feynman diagrams for the ttH production processes. |
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Figure 1-a:
Representative Feynman diagrams for the ttH production processes. |
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Figure 1-b:
Representative Feynman diagrams for the ttH production processes. |
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Figure 2:
Upper (lower) row: representative Feynman diagrams for the tH process in the $ t $-channel ($tW-associated) production mode. |
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Figure 2-a:
Upper (lower) row: representative Feynman diagrams for the tH process in the $ t $-channel ($tW-associated) production mode. |
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Figure 2-b:
Upper (lower) row: representative Feynman diagrams for the tH process in the $ t $-channel ($tW-associated) production mode. |
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Figure 2-c:
Upper (lower) row: representative Feynman diagrams for the tH process in the $ t $-channel ($tW-associated) production mode. |
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Figure 2-d:
Upper (lower) row: representative Feynman diagrams for the tH process in the $ t $-channel ($tW-associated) production mode. |
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Figure 3:
One of the most important input variables for the CP discriminant, $ M_{\mathrm{t}\overline{\mathrm{t}}\mathrm{H}} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 3-a:
One of the most important input variables for the CP discriminant, $ M_{\mathrm{t}\overline{\mathrm{t}}\mathrm{H}} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 3-b:
One of the most important input variables for the CP discriminant, $ M_{\mathrm{t}\overline{\mathrm{t}}\mathrm{H}} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 3-c:
One of the most important input variables for the CP discriminant, $ M_{\mathrm{t}\overline{\mathrm{t}}\mathrm{H}} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 4:
One of the most important input variables for the CP discriminant, $ \Delta \eta_{BB} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 4-a:
One of the most important input variables for the CP discriminant, $ \Delta \eta_{BB} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 4-b:
One of the most important input variables for the CP discriminant, $ \Delta \eta_{BB} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 4-c:
One of the most important input variables for the CP discriminant, $ \Delta \eta_{BB} $, in the three validation regions enriched from left to right in WZ, ttZ and misidentified lepton background. |
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Figure 5:
Most important input variables to the XGBOOST used for CP discrimination in 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 5-a:
Most important input variables to the XGBOOST used for CP discrimination in 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 5-b:
Most important input variables to the XGBOOST used for CP discrimination in 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 5-c:
Most important input variables to the XGBOOST used for CP discrimination in 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 6:
Most important input variables to the XGBOOST used for CP discrimination in 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 6-a:
Most important input variables to the XGBOOST used for CP discrimination in 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 6-b:
Most important input variables to the XGBOOST used for CP discrimination in 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 6-c:
Most important input variables to the XGBOOST used for CP discrimination in 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ channel, defined in Table 4. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Figure 7:
Diagram showing the categorization strategy used for the signal extraction, making use of MVA-based algorithms and topological variables. In addition to the three signal regions (SRs), the ML fit receives input from two control regions (CRs). |
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Figure 8:
Postfit discriminating distributions used as input to the fit. Events in the ttH node are categorized as described in Section 8 for the three categories: 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ (top) 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ (center) and 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ (bottom). For the 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ bl (bt) denotes events with less than (at least) two b-tagged jets. The ttH CP-even (red) and CP-odd (pink) contributions are determined from the fit. The contribution labeled as Nonprompt refers to the backgrounds arising from misidentified leptons while the label Charge mism. alludes to to the backgrounds arising from lepton charge mismeasurement. |
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Figure 8-a:
Postfit discriminating distributions used as input to the fit. Events in the ttH node are categorized as described in Section 8 for the three categories: 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ (top) 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ (center) and 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ (bottom). For the 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ bl (bt) denotes events with less than (at least) two b-tagged jets. The ttH CP-even (red) and CP-odd (pink) contributions are determined from the fit. The contribution labeled as Nonprompt refers to the backgrounds arising from misidentified leptons while the label Charge mism. alludes to to the backgrounds arising from lepton charge mismeasurement. |
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Figure 8-b:
Postfit discriminating distributions used as input to the fit. Events in the ttH node are categorized as described in Section 8 for the three categories: 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ (top) 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ (center) and 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ (bottom). For the 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ bl (bt) denotes events with less than (at least) two b-tagged jets. The ttH CP-even (red) and CP-odd (pink) contributions are determined from the fit. The contribution labeled as Nonprompt refers to the backgrounds arising from misidentified leptons while the label Charge mism. alludes to to the backgrounds arising from lepton charge mismeasurement. |
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Figure 8-c:
Postfit discriminating distributions used as input to the fit. Events in the ttH node are categorized as described in Section 8 for the three categories: 2$\ell$SS$+$0$\tau_{\mathrm{h}}$ (top) 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ (center) and 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ (bottom). For the 2$\ell$SS$+$1$\tau_{\mathrm{h}}$ bl (bt) denotes events with less than (at least) two b-tagged jets. The ttH CP-even (red) and CP-odd (pink) contributions are determined from the fit. The contribution labeled as Nonprompt refers to the backgrounds arising from misidentified leptons while the label Charge mism. alludes to to the backgrounds arising from lepton charge mismeasurement. |
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Figure 9:
Likelihood scan as a function of $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $: expected limits (left) and observed limits (right). The black cross shows the best value for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $ given by the fit. The black diamond shows the expected SM values for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $. Both 68 and 95% CL limits are shown. $ \kappa_{\text{V}} $ and H boson branching fractions are kept to their SM values. |
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Figure 9-a:
Likelihood scan as a function of $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $: expected limits (left) and observed limits (right). The black cross shows the best value for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $ given by the fit. The black diamond shows the expected SM values for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $. Both 68 and 95% CL limits are shown. $ \kappa_{\text{V}} $ and H boson branching fractions are kept to their SM values. |
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Figure 9-b:
Likelihood scan as a function of $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $: expected limits (left) and observed limits (right). The black cross shows the best value for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $ given by the fit. The black diamond shows the expected SM values for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $. Both 68 and 95% CL limits are shown. $ \kappa_{\text{V}} $ and H boson branching fractions are kept to their SM values. |
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Figure 10:
Likelihood scan as a function of $ |f_{CP}^{\mathrm{H}\mathrm{t}\mathrm{t}}| $ for multilepton final estates. The solid (dashed) line shows the observed (expected) scan. |
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Figure 11:
Likelihood scan as a function of $ |f_{CP}^{\mathrm{H}\mathrm{t}\mathrm{t}}| $. The left plot shows the expected likelihood scan for multilepton final states, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states, and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. The right plot shows the observed likelihood scan for multilepton final states and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. |
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Figure 11-a:
Likelihood scan as a function of $ |f_{CP}^{\mathrm{H}\mathrm{t}\mathrm{t}}| $. The left plot shows the expected likelihood scan for multilepton final states, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states, and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. The right plot shows the observed likelihood scan for multilepton final states and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. |
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Figure 11-b:
Likelihood scan as a function of $ |f_{CP}^{\mathrm{H}\mathrm{t}\mathrm{t}}| $. The left plot shows the expected likelihood scan for multilepton final states, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states, and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. The right plot shows the observed likelihood scan for multilepton final states and the combination of multilepton, $ \mathrm{H}\to\gamma\gamma $, and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ final states. |
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Figure 12:
Likelihood scan as a function of $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $. Two-dimensional confidence intervals at 68% CL are depicted as shaded areas, for multilepton (red), the combination of $ \mathrm{H}\to\gamma\gamma $ and $ \mathrm{H}\to\mathrm{Z}\mathrm{Z} $ (blue), and the combination of the three channels (black). The 95% CL for the combination is show as a dashed line. The best fit for each is shown as a cross of the corresponding colour. The plot is symmetric with respect to the line $ \tilde{\kappa}_{\mathrm{t}} =$ 0, hence there are two points corresponding to the best fit, here we only show one for simplicity. The black diamond shows the SM expected value. The nontrivial correlation between the measurements are the source of the change in the best fit value and shape of the confidence regions. The coupling $ \kappa_{\text{V}} $ and the H boson branching fractions are kept to their SM values. |
Tables | |
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Table 1:
Possible CP scenarios |
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Table 2:
Standard model cross sections for the ttH and tH signals as well as for the most relevant background processes estimated from simulation. The cross sections are quoted for pp collisions at $ \sqrt{s} = $ 13 TeV. |
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Table 3:
Event selections applied in the 2$\ell$SS$+$0$\tau_{\mathrm{h}}$, 2$\ell$SS$+$1$\tau_{\mathrm{h}}$, and 3$\ell$SS$+$0$\tau_{\mathrm{h}}$ categories. |
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Table 4:
Input features for the three BDTs. A check mark indicates the variable is used in a given final state, whereas a long dash indicates the variable is not used in that final state. |
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Table 5:
Summary of the uncertainty sources, their type, and their correlations across the three data-taking periods. Trigger efficiency uncertainty is taken as a shape or normalization systematic depending on the channel. |
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Table 6:
One-dimensional confidence intervals at 68 and 95% CL for $ \kappa_{\mathrm{t}} $ (fixing $ \tilde{\kappa}_{\mathrm{t}} $ to the SM) and $ \tilde{\kappa}_{\mathrm{t}} $ (fixing $ \kappa_{\mathrm{t}} $ to the SM). The upper part of the table shows the expected limits while the lower part shows the observed limits. |
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Table 7:
One-dimensional confidence intervals at 68 and 95% CL for $ \kappa_{\mathrm{t}} $ and $ \tilde{\kappa}_{\mathrm{t}} $. |
Summary |
A measurement of the charge-parity (CP) structure of the Yukawa coupling between the Higgs (H) boson and top quarks at tree level, when the H boson is produced in association with one (tH) or two (ttH) top quarks, is presented. The measurement is based on data collected in proton-proton collisions at $\sqrt{s} = $ 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis targets events where the H boson decays to leptons and the top quark(s) decay either leptonically or hadronically. Separation of CP-even from CP-odd scenarios is achieved by applying machine learning techniques to final states characterized by the presence of at least two leptons. Two-dimensional confidence regions are set on ${\kappa_{\mathrm{t}}}$ and ${\tilde{\kappa}_{\mathrm{t}}}$ which are respectively the CP-even and CP-odd top-Higgs Yukawa coupling modifiers: one-dimensional confidence intervals are also set, constraining ${\kappa_{\mathrm{t}}}$ to be within ($-$1.09, $-$0.74) or (0.77, 1.30) and ${\tilde{\kappa}_{\mathrm{t}}}$ to be within ($-$1.4, 1.4) at 95% confidence level (CL). No significant CP-odd contribution is observed, and the corresponding fraction parameter is determined to be ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} =$ 0.59 with an interval of (0.24, 0.81) at 68% CL. The results are combined with previously published analyses covering the H $\to$ ZZ and H $\to\gamma\gamma$ decay modes. Two- and one-dimensional confidence regions are set on ${\kappa_{\mathrm{t}}}$ and ${\tilde{\kappa}_{\mathrm{t}}}$, constraining ${\kappa_{\mathrm{t}}}$ to be within (0.86, 1.26) and ${\tilde{\kappa}_{\mathrm{t}}}$ to be within ($-$1.07, 1.07) at 95% CL. The possibility of a CP-odd contribution is also investigated in the combination, yielding a best fit of ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} =$ 0.28 with an interval of ${|{f_{\mathrm{CP}}^{\mathrm{H}\mathrm{t}\mathrm{t}}}|} <$ 0.55 at 68% CL. The results are compatible with predictions for the standard model H boson. |
Additional Figures | |
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Additional Figure 1:
Output of the XGBOOST used for CP discrimination in 2$ \ell$SS+0$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 2:
Output of the XGBOOST used for CP discrimination in 3$ \ell$+0$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 3:
Output of the XGBOOST used for CP discrimination in 2$ \ell$SS+1$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 4:
Most important input variables to the XGBOOST used for CP discrimination in 2$ \ell$SS+1$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 4-a:
$M_{\mathrm{t\bar{t}H}}$, one of the most important input variables to the XGBOOST used for CP discrimination in 2$ \ell$SS+1$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 4-b:
Minimum $\Delta R_{\text{jet-leading lepton}}$, one of the most important input variables to the XGBOOST used for CP discrimination in 2$ \ell$SS+1$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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Additional Figure 4-c:
Average $\Delta R_{\text{jet-jet}}$, one of the most important input variables to the XGBOOST used for CP discrimination in 2$ \ell$SS+1$\tau_\mathrm{h} $ channel. The vertical bars represent the statistical uncertainty originating from the limited amount of simulated events. When not visible, the bars are smaller than the line width. |
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