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| CMS-PAS-TOP-21-003 | ||
| Search for new physics using top quark pairs produced in association with a boosted Z or Higgs boson in effective field theory | ||
| CMS Collaboration | ||
| February 2022 | ||
| Abstract: A data sample containing top quark pairs produced in association with a boosted Z or Higgs boson is used to search for signs of new physics. The data correspond to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions produced at a center-of-mass energy of 13 TeV at the LHC and collected by the CMS experiment. Selected collision events contain a single lepton and hadronic jets, including two identified with the decay of bottom quarks, plus an additional large-radius jet with high transverse momentum identified as a Z or Higgs boson candidate decaying to a bottom quark pair. Machine learning techniques are employed to discriminate between $\mathrm{t}\bar{\mathrm{t}}$Z or $\mathrm{t}\bar{\mathrm{t}}$H events and events from background processes, which are dominated by $\mathrm{t}\bar{\mathrm{t}}$+jets production. The signal strengths of boosted $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H processes are measured, and upper limits are placed on the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H differential cross sections as functions of the Z or Higgs boson transverse momentum. In addition, effects of physics beyond the standard model are probed using a framework in which the standard model is considered to be the low-energy effective field theory of a higher-scale theory. Eight possible dimension-six operators are added to the standard model Lagrangian and their corresponding coefficients are constrained via a fit to the data. | ||
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Links:
CDS record (PDF) ;
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These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Example tree-level Feynman diagrams for the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H production processes. |
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Figure 1-a:
Example tree-level Feynman diagrams for the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H production processes. |
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Figure 1-b:
Example tree-level Feynman diagrams for the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H production processes. |
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Figure 2:
The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H cross sections in the SM EFT, as ratios to the corresponding SM cross sections, as a function of $ {{c_{{\mathrm {t}} {\mathrm {Z}}}}} /{\Lambda}^{2}$ and the Z boson ${p_{\mathrm {T}}}$ (left), and as a function of $ {{c_{\varphi {\mathrm {t}} {\mathrm {b}}}}} /{\Lambda}^{2}$ and the Higgs boson ${p_{\mathrm {T}}}$ (right). |
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Figure 2-a:
The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H cross sections in the SM EFT, as ratios to the corresponding SM cross sections, as a function of $ {{c_{{\mathrm {t}} {\mathrm {Z}}}}} /{\Lambda}^{2}$ and the Z boson ${p_{\mathrm {T}}}$ (left), and as a function of $ {{c_{\varphi {\mathrm {t}} {\mathrm {b}}}}} /{\Lambda}^{2}$ and the Higgs boson ${p_{\mathrm {T}}}$ (right). |
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Figure 2-b:
The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H cross sections in the SM EFT, as ratios to the corresponding SM cross sections, as a function of $ {{c_{{\mathrm {t}} {\mathrm {Z}}}}} /{\Lambda}^{2}$ and the Z boson ${p_{\mathrm {T}}}$ (left), and as a function of $ {{c_{\varphi {\mathrm {t}} {\mathrm {b}}}}} /{\Lambda}^{2}$ and the Higgs boson ${p_{\mathrm {T}}}$ (right). |
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Figure 3:
The DNN score distribution for well-reconstructed $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal events in which the reconstructed Z or Higgs boson candidate is matched to both generator-level daughter b quarks of the Z or Higgs boson, the remaining $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events, and ${{\mathrm {t}\overline {\mathrm {t}}}}$ + ${\mathrm {b}} {\overline {\mathrm {b}}}$, ${{\mathrm {t}\overline {\mathrm {t}}}}$ + ${\mathrm {c}} {\overline {\mathrm {c}}}$, and ${{\mathrm {t}\overline {\mathrm {t}}}}$ + LF background events. The events shown here satisfy the baseline selection requirements described in Section 4 and contain a Z or Higgs boson candidate with $ {p_{\mathrm {T}}} > $ 300 GeV. |
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Figure 4:
Soft-drop mass distributions of Z/H $ \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ candidate jets in three ${p_{\mathrm {T}}}$ ranges: 200-300 GeV (upper), 300-450 GeV (middle), and above 450 GeV (lower) in simulated samples. The signal distributions are scaled up by a factor of ten for easier comparison with the backgrounds. The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H distributions include well-reconstructed $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events as well as $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events that either do not contain $ {\mathrm {Z}} / {\mathrm {H}} \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ or are not well reconstructed. The red hatched bands correspond to the statistical uncertainty in the background. |
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Figure 4-a:
Soft-drop mass distributions of Z/H $ \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ candidate jets in three ${p_{\mathrm {T}}}$ ranges: 200-300 GeV (upper), 300-450 GeV (middle), and above 450 GeV (lower) in simulated samples. The signal distributions are scaled up by a factor of ten for easier comparison with the backgrounds. The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H distributions include well-reconstructed $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events as well as $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events that either do not contain $ {\mathrm {Z}} / {\mathrm {H}} \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ or are not well reconstructed. The red hatched bands correspond to the statistical uncertainty in the background. |
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Figure 4-b:
Soft-drop mass distributions of Z/H $ \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ candidate jets in three ${p_{\mathrm {T}}}$ ranges: 200-300 GeV (upper), 300-450 GeV (middle), and above 450 GeV (lower) in simulated samples. The signal distributions are scaled up by a factor of ten for easier comparison with the backgrounds. The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H distributions include well-reconstructed $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events as well as $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events that either do not contain $ {\mathrm {Z}} / {\mathrm {H}} \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ or are not well reconstructed. The red hatched bands correspond to the statistical uncertainty in the background. |
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Figure 4-c:
Soft-drop mass distributions of Z/H $ \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ candidate jets in three ${p_{\mathrm {T}}}$ ranges: 200-300 GeV (upper), 300-450 GeV (middle), and above 450 GeV (lower) in simulated samples. The signal distributions are scaled up by a factor of ten for easier comparison with the backgrounds. The $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H distributions include well-reconstructed $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events as well as $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events that either do not contain $ {\mathrm {Z}} / {\mathrm {H}} \to {{\mathrm {b}} {\overline {\mathrm {b}}}} $ or are not well reconstructed. The red hatched bands correspond to the statistical uncertainty in the background. |
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Figure 5:
The percentage of simulated $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) signal events that satisfy the baseline event selection requirements as well as the DNN and mass requirements in bins defined by the reconstructed AK8 jet ${p_{\mathrm {T}}}$ ($x$ axis) and simulated $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ ($y$ axis). The rightmost and topmost bins are unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. The $z$-axis value in each bin is the ratio of the event yield in the bin to the total number of simulated signal events in that $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ bin. |
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Figure 5-a:
The percentage of simulated $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) signal events that satisfy the baseline event selection requirements as well as the DNN and mass requirements in bins defined by the reconstructed AK8 jet ${p_{\mathrm {T}}}$ ($x$ axis) and simulated $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ ($y$ axis). The rightmost and topmost bins are unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. The $z$-axis value in each bin is the ratio of the event yield in the bin to the total number of simulated signal events in that $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ bin. |
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Figure 5-b:
The percentage of simulated $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) signal events that satisfy the baseline event selection requirements as well as the DNN and mass requirements in bins defined by the reconstructed AK8 jet ${p_{\mathrm {T}}}$ ($x$ axis) and simulated $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ ($y$ axis). The rightmost and topmost bins are unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. The $z$-axis value in each bin is the ratio of the event yield in the bin to the total number of simulated signal events in that $ {p_{\mathrm {T}}} ^{{\mathrm {Z}} / {\mathrm {H}}}$ bin. |
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Figure 6:
Post-fit expected and observed yields for the 2016, 2017, and 2018 data-taking periods (from top to bottom) in each analysis bin. In the fit, the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal cross sections are fixed to the SM predictions. The analysis bins are defined as functions of the DNN score, and the ${p_{\mathrm {T}}}$ and ${m_\text {SD}}$ of the boson candidate AK8 jet. The largest groupings of bins are defined by the AK8 jet ${p_{\mathrm {T}}}$. The smaller groups are defined by the DNN score, and the smallest groups, 3 or 4 bins with the same ${p_{\mathrm {T}}}$ and DNN score, correspond to the AK8 jet ${m_\text {SD}}$. |
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Figure 6-a:
Post-fit expected and observed yields for the 2016, 2017, and 2018 data-taking periods (from top to bottom) in each analysis bin. In the fit, the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal cross sections are fixed to the SM predictions. The analysis bins are defined as functions of the DNN score, and the ${p_{\mathrm {T}}}$ and ${m_\text {SD}}$ of the boson candidate AK8 jet. The largest groupings of bins are defined by the AK8 jet ${p_{\mathrm {T}}}$. The smaller groups are defined by the DNN score, and the smallest groups, 3 or 4 bins with the same ${p_{\mathrm {T}}}$ and DNN score, correspond to the AK8 jet ${m_\text {SD}}$. |
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Figure 6-b:
Post-fit expected and observed yields for the 2016, 2017, and 2018 data-taking periods (from top to bottom) in each analysis bin. In the fit, the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal cross sections are fixed to the SM predictions. The analysis bins are defined as functions of the DNN score, and the ${p_{\mathrm {T}}}$ and ${m_\text {SD}}$ of the boson candidate AK8 jet. The largest groupings of bins are defined by the AK8 jet ${p_{\mathrm {T}}}$. The smaller groups are defined by the DNN score, and the smallest groups, 3 or 4 bins with the same ${p_{\mathrm {T}}}$ and DNN score, correspond to the AK8 jet ${m_\text {SD}}$. |
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Figure 6-c:
Post-fit expected and observed yields for the 2016, 2017, and 2018 data-taking periods (from top to bottom) in each analysis bin. In the fit, the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal cross sections are fixed to the SM predictions. The analysis bins are defined as functions of the DNN score, and the ${p_{\mathrm {T}}}$ and ${m_\text {SD}}$ of the boson candidate AK8 jet. The largest groupings of bins are defined by the AK8 jet ${p_{\mathrm {T}}}$. The smaller groups are defined by the DNN score, and the smallest groups, 3 or 4 bins with the same ${p_{\mathrm {T}}}$ and DNN score, correspond to the AK8 jet ${m_\text {SD}}$. |
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Figure 7:
The observed best-fit signal strengths modifiers $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}}$ versus $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$ for simulated Z or Higgs boson $ {p_{\mathrm {T}}} > $ 200 GeV. The contours show the 68 and 95% CL regions. |
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Figure 8:
Observed and expected 95% CL upper limits on the $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) differential cross sections as a function of Z and Higgs boson ${p_{\mathrm {T}}}$. The green and yellow bands show the expected 95% CL upper limits while the black lines represent the observed 95% CL upper limits. The magenta lines show the SM predicted differential cross section with PDF + ${\alpha _S} $ and QCD scale uncertainties. The lower panel shows the ratio of the expected and observed upper limits on the differential cross sections to the SM differential cross section. The last bin is unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. |
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Figure 8-a:
Observed and expected 95% CL upper limits on the $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) differential cross sections as a function of Z and Higgs boson ${p_{\mathrm {T}}}$. The green and yellow bands show the expected 95% CL upper limits while the black lines represent the observed 95% CL upper limits. The magenta lines show the SM predicted differential cross section with PDF + ${\alpha _S} $ and QCD scale uncertainties. The lower panel shows the ratio of the expected and observed upper limits on the differential cross sections to the SM differential cross section. The last bin is unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. |
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Figure 8-b:
Observed and expected 95% CL upper limits on the $\mathrm{t}\bar{\mathrm{t}}$Z (left) and $\mathrm{t}\bar{\mathrm{t}}$H (right) differential cross sections as a function of Z and Higgs boson ${p_{\mathrm {T}}}$. The green and yellow bands show the expected 95% CL upper limits while the black lines represent the observed 95% CL upper limits. The magenta lines show the SM predicted differential cross section with PDF + ${\alpha _S} $ and QCD scale uncertainties. The lower panel shows the ratio of the expected and observed upper limits on the differential cross sections to the SM differential cross section. The last bin is unbounded, extending to $ {p_{\mathrm {T}}} =\infty $. |
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Figure 9:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-a:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-b:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-c:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-d:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-e:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-f:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-g:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 9-h:
Observed (black) and expected (red) one-dimensional scans of the negative log-likelihood as a function of each of the eight WCs when the seven other WCs are fixed to their SM values. The 68 and 95% CL intervals are indicated by thin gray lines. |
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Figure 10:
The observed 68 and 95% CL intervals for the WCs. The intervals are found by scanning over a single WC while either treating the other seven as profiled, or fixing the other seven to the SM value of zero. |
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Figure 11:
Observed two-dimensional scans of the negative log-likelihood as a function of two of the eight WCs when all other WCs are fixed to their SM values. The pair of WCs scanned correspond to the three highest observed correlation coefficients out of all pairs. They are ${{c_{\varphi {\mathrm {t}}}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper left), ${{c^{3}_{\varphi Q}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper right), and ${{c_{{\mathrm {t}} {\mathrm {W}}}}}$ versus ${{c_{{\mathrm {t}} {\mathrm {Z}}}}}$ (lower). The 68, 95, and 99.7% CL intervals are indicated by the yellow, blue, and green lines respectively. |
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Figure 11-a:
Observed two-dimensional scans of the negative log-likelihood as a function of two of the eight WCs when all other WCs are fixed to their SM values. The pair of WCs scanned correspond to the three highest observed correlation coefficients out of all pairs. They are ${{c_{\varphi {\mathrm {t}}}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper left), ${{c^{3}_{\varphi Q}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper right), and ${{c_{{\mathrm {t}} {\mathrm {W}}}}}$ versus ${{c_{{\mathrm {t}} {\mathrm {Z}}}}}$ (lower). The 68, 95, and 99.7% CL intervals are indicated by the yellow, blue, and green lines respectively. |
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Figure 11-b:
Observed two-dimensional scans of the negative log-likelihood as a function of two of the eight WCs when all other WCs are fixed to their SM values. The pair of WCs scanned correspond to the three highest observed correlation coefficients out of all pairs. They are ${{c_{\varphi {\mathrm {t}}}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper left), ${{c^{3}_{\varphi Q}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper right), and ${{c_{{\mathrm {t}} {\mathrm {W}}}}}$ versus ${{c_{{\mathrm {t}} {\mathrm {Z}}}}}$ (lower). The 68, 95, and 99.7% CL intervals are indicated by the yellow, blue, and green lines respectively. |
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Figure 11-c:
Observed two-dimensional scans of the negative log-likelihood as a function of two of the eight WCs when all other WCs are fixed to their SM values. The pair of WCs scanned correspond to the three highest observed correlation coefficients out of all pairs. They are ${{c_{\varphi {\mathrm {t}}}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper left), ${{c^{3}_{\varphi Q}}}$ versus ${{c^{-}_{\varphi Q}}}$ (upper right), and ${{c_{{\mathrm {t}} {\mathrm {W}}}}}$ versus ${{c_{{\mathrm {t}} {\mathrm {Z}}}}}$ (lower). The 68, 95, and 99.7% CL intervals are indicated by the yellow, blue, and green lines respectively. |
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Figure 12:
The observed 95% CL intervals for the WCs. The intervals are found by scanning over a single WC while fixing the other seven to zero. For comparison, we also show the corresponding 95% CL intervals from Refs. [CMS-TOP-18-009,CMS-TOP-19-001,CMS-TOP-21-001,CMS-TOP-21-004]. |
| Tables | |
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Table 1:
The set of EFT operators considered in this analysis that affect the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H processes at order 1$/\Lambda ^2$. The couplings are restricted to involve only third-generation quarks. The quantity $\gamma ^\mu $ denotes the Dirac matrices, $\sigma ^{\mu \nu}$ denotes the Dirac sigma matrices, and $\tau ^I$ denotes the Pauli matrices. The field $\varphi $ is the Higgs boson doublet, and $\tilde{\varphi}^{j}=\varepsilon _{jk} (\varphi ^{k} )^*$, where $\varepsilon $ is the Levi-Civita symbol and $\varepsilon _{12} = $ $+$1. The quark doublet is represented by q, and u and d represent the right-handed quark singlets. Furthermore, $(\varphi ^{\dagger}i\overleftrightarrow {D}_\mu \varphi) \equiv \varphi ^\dagger (iD_\mu \varphi)-(iD_\mu \varphi ^\dagger)\varphi $ and $(\varphi ^{\dagger}i\overleftrightarrow {D}^I_\mu \varphi) \equiv \varphi ^{\dagger}\tau ^I(iD_\mu \varphi)-(iD_\mu \varphi ^\dagger)\tau ^I\varphi $, where $D_{\mu}$ is the covariant derivative. The symbols $ {\mathrm {W}}_{\mu \nu}^I$ and $ {{\mathrm {B}}}_{\mu \nu}$ denote the field strength tensors for the weak isospin and weak hypercharge gauge fields. The abbreviations ${\mathcal {S}_{\mathrm {W}}}$ and ${\mathcal {C}_{\mathrm {W}}}$ denote the sine and cosine of the weak mixing angle in the unitary gauge, respectively. |
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Table 2:
Summary of the reconstructed object and event selection requirements. |
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Table 3:
The expected and observed best-fit signal strength modifiers $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}}$ and $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$ for simulated Z or Higgs boson $ {p_{\mathrm {T}}} > $ 200 GeV. The observed uncertainties are broken down into the components arising from the limited size of the data, the limited size of the simulation samples, experimental uncertainties, and theoretical uncertainties. |
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Table 4:
Major sources of uncertainty in the measurement of the signal strength modifiers $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}}$ and $\mu _{{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$ for simulated Z or Higgs boson $ {p_{\mathrm {T}}} > $ 200 GeV. |
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Table 5:
Observed (median expected ${\pm}$1 standard deviation) 95% CL upper limits for $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H differential cross sections. |
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Table 6:
Observed 95% CL intervals on the eight WCs in the EFT model. The intervals are determined by scanning over a single WC while either treating the other seven as profiled, or fixing the other seven to the SM value of zero. |
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Table 7:
Comprehensive list of the neural network input variables. The "+'' represents the relativistic four-momentum sum. Some variables are calculated for both the highest ${p_{\mathrm {T}}}$ (leading) and second-highest ${p_{\mathrm {T}}}$ (subleading) jet as indicated. |
| Summary |
|
A measurement of the signal strengths and 95% confidence level (CL) upper limits on the differential cross sections for production of boosted $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H events are presented along with constraints on the parameters of a leading-order effective field theory. The analysis is performed using the $\mathrm{b\bar{b}}$ decay mode of the Z or Higgs boson and the semileptonic decay mode of the associated $\mathrm{t\bar{t}}$ pair. The Z or Higgs boson is required to be highly boosted, with ${p_{\mathrm{T}}} > $ 200 GeV. A deep neural network is employed to discriminate between the $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H signal events and the background, which is dominated by$\mathrm{t}\bar{\mathrm{t}}$+jets production. The data correspond to an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the CERN LHC from 2016 through 2018. The data are binned as a function of the reconstructed ${p_{\mathrm{T}}}$ and mass of the Z or Higgs boson, and the score provided by the global event neural network. Binned maximum likelihood fits are employed to extract the observables from the data. The data are found to be consistent with and fit well to expectations from the standard model. The signal strength modifiers for boosted $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H production are measured to be $\mu_{{\mathrm{t\bar{t}}\mathrm{Z}} } = $ 0.65$^{+1.05}_{-0.98}$ and $\mu_{{\mathrm{t\bar{t}}\mathrm{H}} } = $ $-$0.33$^{+0.87}_{-0.85}$ at the 68% CL. The 95% CL upper limits on the differential $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H cross sections are found to range from 2 to 5 times the SM predicted cross sections when the Z or Higgs boson has ${p_{\mathrm{T}}} > $ 300 GeV. Results are also presented on the eight parameters of a leading-order effective field theory, which have a large impact on the boosted $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H production. These results represent the most restrictive limits to date on the cross sections for the production of $\mathrm{t}\bar{\mathrm{t}}$Z and $\mathrm{t}\bar{\mathrm{t}}$H with Z or Higgs boson ${p_{\mathrm{T}}} > $ 450 GeV, as well as stringent constraints on the Wilson coefficients $c_{\mathrm{t}\varphi}$, $c_{\varphi\mathrm{tb}}$, $c_{\mathrm{bW}}$, and $c_{\mathrm{tW}}$ in effective field theory. |
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