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| CMS-B2G-22-001 ; CERN-EP-2026-047 | ||
| Search for a new heavy resonance decaying to a top quark and a neutral scalar boson in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 12 April 2026 | ||
| Submitted to Physics Letters B | ||
| Abstract: A first search at the LHC for a new heavy resonance decaying to a top quark and a neutral scalar boson $ \phi $ in the fully hadronic final state is presented, where the $ \phi $ boson is identified by its decay into a bottom quark-antiquark pair. The search is focused on final states in which the decay products of the highly Lorentz boosted top quark and $ \phi $ boson are each reconstructed as a single, large-radius jet with distinct substructure. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $, recorded with the CMS detector at the LHC in 2016--2018. The single production of a vector-like top quark, T', is used as a benchmark model for the signal process. The results of this search are combined with those of a previous CMS search in which semileptonic decays of the top quark were used. No significant excess of data is observed with respect to the background prediction. For the case where the neutral scalar is a standard model Higgs boson and the T' quark width is 5% of its mass, T' quark masses between 0.85 and 1.3 TeV are excluded at 95% confidence level and the most stringent limits to date are set for masses above 2 TeV. For other $ \phi $ boson masses, upper limits as low as 0.1 fb are set on the product of the T' quark production cross section and branching fraction for its decay to a top quark and a $ \phi $ boson. | ||
| Links: e-print arXiv:2604.10729 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Postfit distributions of data and predicted background in the $ \mathrm{SR} $ under the background-only hypothesis, projected onto the $ m_{\phi}^{\text{rec}} $ (left) and $ m_{T'}^{\text{rec}} $ (right) axes in the $ \mathrm{T}_\text{Xbb} $ Pass tagging region, $ \mathrm{SR}_{\mathrm{P}} $. A $ m_{\phi}=175 \text{GeV}, m_{T'}= $ 1100 GeV signal sample normalized to a cross section of 220 $ $ fb is overlaid for visualization. The $ y $ axes of the top panels have been rescaled to display the number of events per bin, divided by the width of each bin. The lower panels show the pull distributions, defined for each bin as the difference between the observed data and the postfit background prediction divided by the square root of the difference between the squared Poisson uncertainty in the data and the squared postfit uncertainty in the total background estimate in that particular bin. |
png pdf |
Figure 1-a:
Postfit distributions of data and predicted background in the $ \mathrm{SR} $ under the background-only hypothesis, projected onto the $ m_{\phi}^{\text{rec}} $ (left) and $ m_{T'}^{\text{rec}} $ (right) axes in the $ \mathrm{T}_\text{Xbb} $ Pass tagging region, $ \mathrm{SR}_{\mathrm{P}} $. A $ m_{\phi}=175 \text{GeV}, m_{T'}= $ 1100 GeV signal sample normalized to a cross section of 220 $ $ fb is overlaid for visualization. The $ y $ axes of the top panels have been rescaled to display the number of events per bin, divided by the width of each bin. The lower panels show the pull distributions, defined for each bin as the difference between the observed data and the postfit background prediction divided by the square root of the difference between the squared Poisson uncertainty in the data and the squared postfit uncertainty in the total background estimate in that particular bin. |
png pdf |
Figure 1-b:
Postfit distributions of data and predicted background in the $ \mathrm{SR} $ under the background-only hypothesis, projected onto the $ m_{\phi}^{\text{rec}} $ (left) and $ m_{T'}^{\text{rec}} $ (right) axes in the $ \mathrm{T}_\text{Xbb} $ Pass tagging region, $ \mathrm{SR}_{\mathrm{P}} $. A $ m_{\phi}=175 \text{GeV}, m_{T'}= $ 1100 GeV signal sample normalized to a cross section of 220 $ $ fb is overlaid for visualization. The $ y $ axes of the top panels have been rescaled to display the number of events per bin, divided by the width of each bin. The lower panels show the pull distributions, defined for each bin as the difference between the observed data and the postfit background prediction divided by the square root of the difference between the squared Poisson uncertainty in the data and the squared postfit uncertainty in the total background estimate in that particular bin. |
png pdf |
Figure 2:
The upper limit at 95% CL on the product of cross section for the $ T' \to \mathrm{t}\phi $ process and branching fraction $ \mathcal{B}(\mathrm{t}\to \mathrm{b}\mathrm{q}\overline{\mathrm{q}}^\prime) $ as a function of $ (m_{T' },m_{\phi}) $, assuming $ \mathcal{B}(\phi\to\mathrm{b}\overline{\mathrm{b}})=100% $. Masses of the $ \phi $ boson below 75 GeV are exclusive to the semileptonic channel, while $ m_{\phi} > $ 250 GeV are exclusive to the fully hadronic channel. Besides $ m_{\phi}= $ 225 GeV, also exclusive to the fully hadronic channel, upper limits for 75 $ < m_{\phi} < $ 250 GeV are obtained from the combination of the two channels. Gaps in $ m_{\phi} $ above 250 GeV are due to the limitations in the signal interpolation scheme in the hadronic channel, while gaps in $ m_{\phi} < $ 250 GeV correspond to signals not considered by the semileptonic channel due to poor signal efficiency. |
png pdf |
Figure 3:
Upper limits at 95% CL on the product of the cross section and branching fraction for $ \mathrm{p}\mathrm{p}\to T' \to\mathrm{t}\mathrm{H} $ as functions of the T' quark mass for fixed $ m_{\phi}=m_{\mathrm{H}}= $ 125 GeV. In the left panel, the solid blue (brown) curves indicate the theoretical cross sections for the singlet T' quark model assuming its width is 1% (5%) of its mass [34,33]. The contributions to the combination from the semileptonic (red) and fully hadronic (purple) channels are detailed in the right panel, where it is shown that upper limits for T' quark masses below 1 TeV are obtained from the fully hadronic channel only, while limits for all other mass points are obtained from the combination of the semileptonic and fully hadronic channels. The same holds for the shaded 68% and 95% expected upper limits in the right panel. In both panels, the median expected and the observed limits are depicted using dashed and solid lines, respectively. |
png pdf |
Figure 3-a:
Upper limits at 95% CL on the product of the cross section and branching fraction for $ \mathrm{p}\mathrm{p}\to T' \to\mathrm{t}\mathrm{H} $ as functions of the T' quark mass for fixed $ m_{\phi}=m_{\mathrm{H}}= $ 125 GeV. In the left panel, the solid blue (brown) curves indicate the theoretical cross sections for the singlet T' quark model assuming its width is 1% (5%) of its mass [34,33]. The contributions to the combination from the semileptonic (red) and fully hadronic (purple) channels are detailed in the right panel, where it is shown that upper limits for T' quark masses below 1 TeV are obtained from the fully hadronic channel only, while limits for all other mass points are obtained from the combination of the semileptonic and fully hadronic channels. The same holds for the shaded 68% and 95% expected upper limits in the right panel. In both panels, the median expected and the observed limits are depicted using dashed and solid lines, respectively. |
png pdf |
Figure 3-b:
Upper limits at 95% CL on the product of the cross section and branching fraction for $ \mathrm{p}\mathrm{p}\to T' \to\mathrm{t}\mathrm{H} $ as functions of the T' quark mass for fixed $ m_{\phi}=m_{\mathrm{H}}= $ 125 GeV. In the left panel, the solid blue (brown) curves indicate the theoretical cross sections for the singlet T' quark model assuming its width is 1% (5%) of its mass [34,33]. The contributions to the combination from the semileptonic (red) and fully hadronic (purple) channels are detailed in the right panel, where it is shown that upper limits for T' quark masses below 1 TeV are obtained from the fully hadronic channel only, while limits for all other mass points are obtained from the combination of the semileptonic and fully hadronic channels. The same holds for the shaded 68% and 95% expected upper limits in the right panel. In both panels, the median expected and the observed limits are depicted using dashed and solid lines, respectively. |
| Summary |
| A search for single production of a vector-like top quark partner T' decaying to a top quark (t) and a neutral scalar boson $ \phi $ in the fully hadronic final state is presented, using proton-proton collision data recorded by the CMS experiment at $ \sqrt{s}= $ 13 TeV in 2016--2018 and corresponding to a total integrated luminosity of 138 fb$ ^{-1} $. The hadronic decay products of the top quark and $ \phi $ boson are expected to be highly Lorentz boosted from the decay of the massive T' resonance, resulting in two large-radius jets in the final state. The results of this hadronic search are combined with those from a previous search in the semileptonic channels in a simultaneous maximum likelihood fit. No significant excess of data with respect to the background prediction is observed. Upper limits at 95% confidence level (CL) are set on the product of the production cross section and branching fraction for the decay $ T' \to \mathrm{t}\phi $, representing the first results for the decay $ T' \to \mathrm{t} ( \mathrm{b}\mathrm{q}\overline{\mathrm{q}}' )\phi ( \mathrm{b}\overline{\mathrm{b}} ) $ at the LHC. For the case where the neutral scalar is the standard model Higgs boson (H), upper limits are set on the product of the production cross section and the $ T' \to \mathrm{t}\mathrm{H} $ branching fraction between 10 and 0.4$ $ fb at 95% CL for T' quark masses between 1 and 3 TeV. They exclude T' quark masses of 0.85--1.3 TeV assuming the T' quark is a weak-isospin singlet with a resonance width 5% of its mass, improving on all previous searches by the CMS Collaboration [6] by up to a factor of three and representing the most stringent limits to date for masses above 2 TeV. For other $ \phi $ boson masses, upper limits as low as 0.1 fb are set at 95% CL on the product of the T' production cross section and branching fraction to $ \mathrm{t}\phi $. |
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