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| CMS-PAS-B2G-21-007 | ||
| Search of a Vector-Like Quark T' $\to$ tH in the di-photon final state | ||
| CMS Collaboration | ||
| July 2022 | ||
| Abstract: A search for the production of a Vector-Like Quark, T' is presented. The search is based on proton-proton collision events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminonsity of 138 fb$^{-1}$, collected between 2016 and 2018. The search looks specifically for the production of a T' quark which then decays to a top quark and a Higgs boson (T' $\to$ tH); with the Higgs boson subsequently decaying into a pair of photons (H $\to \gamma \gamma$). The top quark can decay either hadronically ($ \mathrm{t \to bq\bar{q} } $) or leptonically ($t \rightarrow bl\nu$). This search presents an upper limit on the T' production cross section for the mass range 600-1200 GeV. No significant excess over the standard model background is observed, accordingly T' masses up to 730 GeV are excluded at 95% confidence level. This search is the first to use the reconstruction of the H $\to \gamma \gamma$ invariant mass, leveraging an experimental resolution of 1-2%. This technique leads to an increased sensitivity to T' mass values up to 1 TeV with respect to the previous searches. | ||
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Links:
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Physics Briefing ;
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These preliminary results are superseded in this paper, JHEP 09 (2023) 057. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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| Figures | |
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Figure 1:
The BDT output distributions for data, backgrounds and signal events in the leptonic and the hadronic categories: (a) Leptonic BDT trained against the SM Higgs boson backgrounds, (b) Hadronic BDT trained against the SM Higgs boson backgrounds, and (c) Hadronic BDT trained against the non-resonant backgrounds processes. For the leptonic category, MC-estimated non-resonant backgrounds is normalized to the number of observed data events. For the hadronic category, data-driven estimation has been adapted for $\gamma $+jets backgrounds, while all other MC samples are normalized to an integrated luminosity of 138 fb$^{-1}$. |
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Figure 1-a:
Leptonic BDT trained against the SM Higgs boson backgrounds: output distributions for data, backgrounds and signal events. MC-estimated non-resonant backgrounds is normalized to the number of observed data events. |
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Figure 1-b:
Hadronic BDT trained against the SM Higgs boson backgrounds: output distributions for data, backgrounds and signal events. Data-driven estimation has been adapted for $\gamma $+jets backgrounds, while all other MC samples are normalized to an integrated luminosity of 138 fb$^{-1}$. |
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Figure 1-c:
Hadronic BDT trained against the non-resonant backgrounds processes: output distributions for data, backgrounds and signal events. Data-driven estimation has been adapted for $\gamma $+jets backgrounds, while all other MC samples are normalized to an integrated luminosity of 138 fb$^{-1}$. |
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Figure 2:
The combined distributions for data and $ {m_{\gamma \gamma}} $ signal-plus-background model fits for VLQ signal with $M_{{{\mathrm T}^\prime}}$ of 600 GeV (left), 900 GeV (middle) and 1200 GeV (right). |
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Figure 2-a:
The combined distributions for data and $ {m_{\gamma \gamma}} $ signal-plus-background model fits for VLQ signal with $M_{{{\mathrm T}^\prime}}$ of 600 GeV. |
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Figure 2-b:
The combined distributions for data and $ {m_{\gamma \gamma}} $ signal-plus-background model fits for VLQ signal with $M_{{{\mathrm T}^\prime}}$ of 900 GeV. |
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Figure 2-c:
The combined distributions for data and $ {m_{\gamma \gamma}} $ signal-plus-background model fits for VLQ signal with $M_{{{\mathrm T}^\prime}}$ of 1200 GeV. |
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Figure 3:
Expected and observed upper limits at 95% CL on $\sigma \times \mathcal{B}({\mathrm{H} \to \gamma \gamma})$ after combining the leptonic and the hadronic channels with $ {m_{{{\mathrm T}^\prime}}} \in $ [600, 1200] GeV. |
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Figure 4:
Observed and expected upper limits at 95% CL on signal strength after combining the leptonic and the hadronic channels with $ {m_{{{\mathrm T}^\prime}}} \in $ [600, 1200] GeV. Sensitivity of other CMS [18,49] and ATLAS [19] searches are also displayed for comparison. |
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Figure 5:
Observed and expected upper limits at 95% CL on $\sigma \times \mathcal{B}({\mathrm{H} \to \gamma \gamma})$ in the leptonic channel with $ {m_{{{\mathrm T}^\prime}}} \in $ [600, 1200] GeV. |
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Figure 6:
Observed and expected upper limits at 95% CL on $\sigma \times \mathcal{B}({\mathrm{H} \to \gamma \gamma})$ in the hadronic channel with $ {m_{{{\mathrm T}^\prime}}} \in $ [600, 1200] GeV. |
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Figure 7:
Observed and expected upper limits at 95% CL on the coupling, $\kappa _T$ with the SM particles under the narrow width approximation (NWA) for $ {m_{{{\mathrm T}^\prime}}} \in $ [600, 1200] GeV. |
| Tables | |
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Table 1:
Selection of the signal region for different T' mass hypotheses and number of events in the $ {m_{\gamma \gamma}} $ side band region, defined by $ {m_{\gamma \gamma}} < $115 || $ {m_{\gamma \gamma}} > $ 135 GeV. |
| Summary |
| A search for the vector-like quark with T' $\to$ tH($\to\gamma\gamma$) has been performed using 138 fb$^{-1}$ of proton-proton collisions (at $\sqrt{s}=$ 13 TeV) data recorded with the CMS detector during LHC Run 2 (2016-2018). The search considers both the hadronic and leptonic decay modes of the top quark and exploits Boosted Decision Trees to separate likely signal events from background processes, including standard model Higgs boson production processes. No statistically significant excess over the expected background prediction is observed; accordingly, T' masses up to 730 GeV have been excluded at 95% CL. |
| Additional Figures | |
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Additional Figure 1:
Expected and observed upper limits at 95% CL on singlet $ \mathrm{T}^\prime $ production signal strength parameter ($ \mu $) after combining the leptonic and the hadronic channels with $ \mathrm{M}_{\mathrm{T}^\prime} \in $ [600, 1200] GeV. Sensitivity of other CMS [18,49] and ATLAS [19] searches are also displayed for comparison. |
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Additional Figure 2:
Reconstructed signal $ \mathrm{T}^\prime $ mass in the hadronic channel with $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} = $ 1%. The number of events reflects the expected signal cross sections as a function of the $ \mathrm{T}^\prime $ mass. The resolutions of the reconstructed signal $ \mathrm{T}^\prime $ masses are in the 5--7% range. |
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Additional Figure 3:
Signal efficiency for the leptonic channel in the signal regions as optimized for each of the three different $ \mathrm{T}^\prime $ mass ranges: [600, 700], [700, 1000] and [1000, 1200] GeV, represented as red, green and blue curves respectively. The efficiency is defined as the ratio of the events after the final selection to the total expected events. |
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Additional Figure 4:
Signal efficiency for the hadronic channel in the signal regions as optimized for each of the three different $ \mathrm{T}^\prime $ mass ranges: [600, 700], [700, 1000] and [1000, 1200] GeV, represented as red, green and blue curves respectively. The efficiency is defined as the ratio of the events after the final selection to the total expected events. |
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Additional Figure 5:
The combined expected (dotted black) and observed (solid black) upper limits at 95% CL on $ \sigma_{\mathrm{T}^\prime\mathrm{b}\mathrm{q}(\mathrm{T}^\prime\rightarrow \mathrm{t}\mathrm{H})} $ displayed as a function of $ \mathrm{M}_{\mathrm{T}^\prime} $. The red dashed lines illustrate theoretical cross sections for the singlet $ \mathrm{T}^\prime $ production with $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} $ = 1 and 5%. The theoretical cross sections of the singlet $ \mathrm{T}^\prime $ production with representative $ \kappa_T $-values fixed at 0.1, 0.15, 0.2 and 0.25 (for $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} < $ 5%) are shown as red solid lines. |
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Additional Figure 6:
The expected (dotted black) and observed (solid black) upper limits at 95% CL on $ \sigma_{\mathrm{T}^\prime\mathrm{b}\mathrm{q}(\mathrm{T}^\prime\rightarrow \mathrm{t}\mathrm{H})} $ in the leptonic channel displayed as a function of $ \mathrm{M}_{\mathrm{T}^\prime} $. The theoretical cross sections of the singlet $ \mathrm{T}^\prime $ production with representative $ \kappa_T $-values fixed at 0.1, 0.15, 0.2 and 0.25 (for $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} < $ 5%) are shown as solid red lines. |
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Additional Figure 7:
The expected (dotted black) and observed (solid black) upper limits at 95% CL on $ \sigma_{\mathrm{T}^\prime\mathrm{b}\mathrm{q}(\mathrm{T}^\prime\rightarrow \mathrm{t}\mathrm{H})} $ in the hadronic channel displayed as a function $ \mathrm{M}_{\mathrm{T}^\prime} $. The theoretical cross sections of the singlet $ \mathrm{T}^\prime $ production with representative $ \kappa_T $-values fixed at 0.1, 0.15, 0.2 and 0.25 (for $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} < $ 5%) are shown as solid red lines. |
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Additional Figure 8:
The combined expected (dotted black) and observed (solid black) upper limits at 95% CL on the $ \mathrm{T}^\prime $ coupling with the SM particles, $ \kappa_{T} $, under the narrow width approximation (NWA) displayed as a function $ \mathrm{M}_{\mathrm{T}^\prime} $. The theoretical $ \kappa_{T} $ values corresponding to the $ \Gamma/\mathrm{M}_{\mathrm{T}^\prime} $-values fixed at 1, 2, 3, 4, and 5% are shown as red dashed lines. |
| Additional Tables | |
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Additional Table 1:
The expected yields of different processes in each signal window for events with $ M_{T'} \in $ [600, 1200] GeV. Yields are shown for events with 115 $ < m_{\gamma\gamma} < $ 135 GeV, and are calculated from MC samples only. |
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