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| CMS-PAS-B2G-22-005 | ||
| Search for pair production of heavy particles decaying to a top quark and a gluon in the lepton+jets final state at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 20 July 2024 | ||
| Abstract: A search is presented for the pair production of new heavy resonances, each decaying into a top quark or antiquark and a gluon. The analysis uses data recorded with the CMS detector from proton-proton collisions at a center-of-mass energy of 13 TeV, 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 search for a signal. No significant deviations from the standard model predictions are found. Upper limits at 95% confidence level are set on the product of cross section times branching fraction squared for the pair production of two 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. This corresponds to mass exclusion limits up to 1050 and 1700 GeV for spin-1/2 and spin-3/2 $ \mathrm{t}^{*} $ particles, respectively. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representive Feynman diagram of the signal process at leading order. |
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Figure 2:
Distributions in $ S_{\mathrm{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. |
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Figure 3:
Two-dimensional distribution in 1 $1 - s_{\text{DNN}} $ versus $ S_{\mathrm{T}} $ for simulated $ \mathrm{t} \overline{\mathrm{t}} $ events. The function $ f(S_{\mathrm{T}}, 30%) $ (red line) is defined through a 30% selection efficiency of $ \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_{\mathrm{T}} $. |
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Figure 4:
The simulation-based ratios between the $ S_{\mathrm{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the average is the final transfer function used for the nontop background estimation. The statistical uncertainty in the transfer function is shown as a grey band. |
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Figure 4-a:
The simulation-based ratios between the $ S_{\mathrm{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the average is the final transfer function used for the nontop background estimation. The statistical uncertainty in the transfer function is shown as a grey band. |
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Figure 4-b:
The simulation-based ratios between the $ S_{\mathrm{T}} $ distributions in the SRs and CRs for the muon (left) and electron (right) channels. Two functions are fit to each ratio, and the average is the final transfer function used for the nontop background estimation. The statistical uncertainty in the transfer function is shown as a grey band. |
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Figure 5:
Distributions in $ S_{\mathrm{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainty is 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 below the distributions. |
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Figure 5-a:
Distributions in $ S_{\mathrm{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainty is 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 below the distributions. |
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Figure 5-b:
Distributions in $ S_{\mathrm{T}} $ in the VR for the muon (left) and electron (right) channels. The total uncertainty is 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 below the distributions. |
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Figure 6:
Distributions in $ S_{\mathrm{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 6-a:
Distributions in $ S_{\mathrm{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 6-b:
Distributions in $ S_{\mathrm{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. [25], is shown in blue, 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. [25], is shown in blue, assuming $ \mathcal{B}(\mathrm{t}^{*} \to \mathrm{t}\mathrm{g})= $ 1. The results of the previous CMS analysis [29], using data corresponding to an integrated luminosity of 35.9 fb$ ^{-1} $, are shown in red. |
| Summary |
| A search for the pair production of heavy resonances $ \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 obtain a region enriched in potential signal events. With a two-step decorrelation procedure, independence of the deep neural network output from the sensitive variable $ S_{\mathrm{T}} $ has been achieved, where $ S_{\mathrm{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 $ \mathrm{t}^{*}\overline{\mathrm{t}}{}^{*} $ production cross section and branching fraction squared for $ \mathrm{t}^{*} \to \mathrm{t}\mathrm{g} $. These are found 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 lower 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. The results substantially improve the spin-3/2 exclusion limits compared to previous results. |
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