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| CMS-B2G-22-005 ; CERN-EP-2024-266 | ||
| Search for pair production of heavy particles decaying to a top quark and a gluon in the lepton+jets final state in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 27 October 2024 | ||
| Submitted to Eur. Phys. J. C | ||
| Abstract: A search is presented for the pair production of new heavy resonances, each decaying into a top quark (t) or antiquark and a gluon ($ \mathrm{g} $). The analysis uses data recorded with the CMS detector from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Events with one muon or electron, multiple jets, and missing transverse momentum are selected. After using a deep neural network to enrich the data sample with signal-like events, distributions in the scalar sum of the transverse momenta of all reconstructed objects are analyzed in the search for a signal. No significant deviations from the standard model prediction are found. Upper limits at 95% confidence level are set on the product of cross section and branching fraction squared for the pair production of excited top quarks in the $ \mathrm{t}^{*} \to \mathrm{t}\mathrm{g} $ decay channel. The upper limits range from 0.12 pb to 0.8 fb for a $\mathrm{t}^{*}$ with spin-1/2 and from 0.015 pb to 1.0 fb for a $\mathrm{t}^{*}$ with spin-3/2. These correspond to mass exclusion limits up to 1050 and 1700 GeV for spin-1/2 and spin-3/2 $\mathrm{t}^{*}$ particles, respectively. These are the most stringent limits to date on the existence of $ \mathrm{t}^{*} \to \mathrm{t}\mathrm{g} $ resonances. | ||
| Links: e-print arXiv:2410.20601 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative Feynman diagram of the signal process at leading order. |
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Figure 2:
Distributions in $ S_{\text{T}} $ for $ \mathrm{t}^{*} \overline{\mathrm{t}}{}^{*} $ signal samples with different simulated values of $ m_{\mathrm{t}^{*} } $, for spin-1/2 (solid lines) and spin-3/2 (dashed lines) resonances. The distributions were normalized to the same area for each signal. |
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Figure 3:
Two-dimensional distribution in 1 $ - s_{\text{DNN}} $ versus $ S_{\text{T}} $ for simulated $ \mathrm{t} \overline{\mathrm{t}} $ events. The function $ f(S_{\text{T}}, 30%) $ (red line) is determined by specifying a 30% selection efficiency for $ \mathrm{t} \overline{\mathrm{t}} $ events, i.e.,, 30% of the $ \mathrm{t} \overline{\mathrm{t}} $ events are below this function in each bin of $ S_{\text{T}} $. |
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Figure 4:
The simulation-based ratios between the $ S_{\text{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the final transfer function used for the non-t background estimation is taken to be their average. The statistical uncertainties in the transfer functions are shown as grey bands. In the lower panels, the simulation-based ratios, fit functions, and statistical uncertainties are shown relative to the final transfer function. |
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Figure 4-a:
The simulation-based ratios between the $ S_{\text{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the final transfer function used for the non-t background estimation is taken to be their average. The statistical uncertainties in the transfer functions are shown as grey bands. In the lower panels, the simulation-based ratios, fit functions, and statistical uncertainties are shown relative to the final transfer function. |
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Figure 4-b:
The simulation-based ratios between the $ S_{\text{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the final transfer function used for the non-t background estimation is taken to be their average. The statistical uncertainties in the transfer functions are shown as grey bands. In the lower panels, the simulation-based ratios, fit functions, and statistical uncertainties are shown relative to the final transfer function. |
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Figure 5:
Distributions of $ S_{\text{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainties are shown as hatched bands. The signal distributions are scaled to the cross sections predicted by theory. Ratios of data to the expected backgrounds are shown in the lower panels. |
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Figure 5-a:
Distributions of $ S_{\text{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainties are shown as hatched bands. The signal distributions are scaled to the cross sections predicted by theory. Ratios of data to the expected backgrounds are shown in the lower panels. |
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Figure 5-b:
Distributions of $ S_{\text{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainties are shown as hatched bands. The signal distributions are scaled to the cross sections predicted by theory. Ratios of data to the expected backgrounds are shown in the lower panels. |
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Figure 6:
Distributions in $ S_{\text{T}} $ in the SR for the muon (left) and electron (right) channels, after a background-only fit to the data. The signal distributions are scaled to the cross section predicted by the theory. The hatched bands show the post-fit uncertainty band, combining all sources of uncertainty. The ratio of data to the background predictions is shown in the panels below the distributions. |
png pdf |
Figure 6-a:
Distributions in $ S_{\text{T}} $ in the SR for the muon (left) and electron (right) channels, after a background-only fit to the data. The signal distributions are scaled to the cross section predicted by the theory. The hatched bands show the post-fit uncertainty band, combining all sources of uncertainty. The ratio of data to the background predictions is shown in the panels below the distributions. |
png pdf |
Figure 6-b:
Distributions in $ S_{\text{T}} $ in the SR for the muon (left) and electron (right) channels, after a background-only fit to the data. The signal distributions are scaled to the cross section predicted by the theory. The hatched bands show the post-fit uncertainty band, combining all sources of uncertainty. The ratio of data to the background predictions is shown in the panels below the distributions. |
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Figure 7:
Expected and observed 95% CL upper limits on the product of the $ \mathrm{t}^{*} \overline{\mathrm{t}}{}^{*} $ production cross section and the branching fraction squared $ \mathcal{B}^2(\mathrm{t}^{*} \to \mathrm{t}\mathrm{g}) $ for a spin-1/2 $\mathrm{t}^{*}$ as a function of $ m_{\mathrm{t}^{*} } $. The inner (green) and outer (yellow) bands give the central probability intervals containing 68 and 95% of the expected upper limits under the background-only hypothesis. The cross section predicted by theory, following the EFT approach introduced in Ref. [26], is shown as a dotted line, assuming $ \mathcal{B}(\mathrm{t}^{*} \to \mathrm{t}\mathrm{g})= $ 1. |
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Figure 8:
Expected and observed 95% CL upper limits on the product of the $ \mathrm{t}^{*} \overline{\mathrm{t}}{}^{*} $ production cross section and the branching fraction squared $ \mathcal{B}^2(\mathrm{t}^{*} \to \mathrm{t}\mathrm{g}) $ for a spin-3/2 $\mathrm{t}^{*}$ as a function of $ m_{\mathrm{t}^{*} } $. The inner (green) and outer (yellow) bands give the central probability intervals containing 68 and 95% of the expected upper limits under the background-only hypothesis. The cross section predicted by theory, following the EFT approach introduced in Ref. [26], is shown as a dotted line, assuming $ \mathcal{B}(\mathrm{t}^{*} \to \mathrm{t}\mathrm{g})= $ 1. The results of the previous CMS analysis [30], using data corresponding to an integrated luminosity of 35.9 fb$ ^{-1} $, are shown as well. |
| Summary |
| A search for the pair production of heavy top-quark partners $\mathrm{t}^{*}$ has been presented, where the $\mathrm{t}^{*}$ couples predominantly to gluons and decays to a top quark and a gluon, $ \mathrm{t}^{*} \to \mathrm{t}\mathrm{g} $. Both spin-1/2 and spin-3/2 resonances are considered. The analysis uses 13 TeV proton-proton collision data collected by the CMS experiment between 2016 and 2018, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The final state analyzed consists of a lepton with high transverse momentum, missing transverse momentum and several jets. A deep neural network is used to identify potential signal events. With a two-step decorrelation procedure, independence of the deep neural network output from the main observable $ S_{\text{T}} $ has been achieved, where $ S_{\text{T}} $ is the scalar sum of the transverse momenta of the selected lepton and jets, and the missing transverse momentum. No statistically significant deviation from the background prediction was found. Upper limits at 95% confidence level are derived on the product of the $ \mathrm{t}^{*} \overline{\mathrm{t}}{}^{*} $ production cross section and branching fraction squared for $ \mathrm{t}^{*} \to \mathrm{t}\mathrm{g} $. These are between 0.12 pb and 0.8 fb for a spin-1/2 $\mathrm{t}^{*}$ and between 0.015 pb and 1.0 fb for a spin-3/2 $\mathrm{t}^{*}$, depending on the $\mathrm{t}^{*}$ mass. A comparison of these limits with the theory predictions results in mass limits for the $\mathrm{t}^{*}$ resonances, where the existence of a spin-1/2 $\mathrm{t}^{*}$ is excluded below a mass of 1050 GeV and for a spin-3/2 $\mathrm{t}^{*}$ below a mass of 1700 GeV. These are the most stringent limits to date and the first exclusion limit for a spin-1/2 $\mathrm{t}^{*}$ resonance at 13 TeV. The results also substantially improve the spin-3/2 exclusion limits compared to previous results. |
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