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| CMS-TOP-20-007 ; CERN-EP-2021-201 | ||
| Search for flavor-changing neutral current interactions of the top quark and Higgs boson in final states with two photons in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 3 November 2021 | ||
| Phys. Rev. Lett. 129 (2022) 032001 | ||
| Abstract: Proton-proton interactions resulting in final states with two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks (t) and Higgs bosons (H). The analysis is based on data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. No significant excess above the background prediction is observed. Upper limits on the branching fractions ($\mathcal B$) of the top quark decaying to a Higgs boson and an up (u) or charm quark (c) are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 0.019 (0.031)% for $\mathcal B(\mathrm{t} \to \mathrm{H}\mathrm{u})$ and 0.073 (0.051)% for $\mathcal B(\mathrm{t} \to \mathrm{H}\mathrm{c})$. These are the strictest upper limits yet determined. | ||
| Links: e-print arXiv:2111.02219 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative Feynman diagrams for the production modes considered: FCNC associated production of a single top quark with a Higgs boson (ST, left), and ${\mathrm{t} {}\mathrm{\bar{t}}}$ production with the FCNC decay of the top quark to a Higgs boson and an up or charm quark (TT, right). The Higgs boson decay to two photons is considered. The FCNC vertex in each process is denoted with a red circle. |
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Figure 2:
Left: distribution of the BDT-nonres scores used for the hadronic event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions from data (points) and predictions from simulation (colored histograms). The "Other'' category includes contributions from ${\mathrm{t} {}\mathrm{\bar{t}}}$Z, ${\mathrm{t} {}\mathrm{\bar{t}}}$W, WW, WZ, ZZ, and t+$ \gamma $+jets. The "top + H'' category includes ${\mathrm{t} {}\mathrm{\bar{t}}}$H, tHq, and tHW, while the "Other H'' category includes ggH, VBF, WH, and ZH. The nonresonant background histograms are stacked, while the two signal, "Other H'', and "top + H'' distributions are shown separately. Boundaries defining event categories are indicated with dotted lines in the upper panel. Events in the grey shaded region are not considered in the analysis. The lower panel shows the ratio of the data to the sum of the nonresonant background predictions. The simulated signal and background distributions are normalized to the integrated luminosity of the data, assuming a coupling of unity for the signal. Statistical and total (statistical $\oplus $ systematic) background uncertainties are represented by the grey- and red-shaded bands, respectively. The (\gamma) + jets sample of multijet and {\gamma + \text {jets}} events from data is not assigned a systematic uncertainty, as described in the text. Right: hadronic event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions from requirements placed on BDT-nonres (horizontal dotted lines) and BDT-res (vertical dotted lines). The color denotes the $s/\sqrt {b}$ of each category. |
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Figure 2-a:
Distribution of the BDT-nonres scores used for the hadronic event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions from data (points) and predictions from simulation (colored histograms). The "Other'' category includes contributions from ${\mathrm{t} {}\mathrm{\bar{t}}}$Z, ${\mathrm{t} {}\mathrm{\bar{t}}}$W, WW, WZ, ZZ, and t+$ \gamma $+jets. The "top + H'' category includes ${\mathrm{t} {}\mathrm{\bar{t}}}$H, tHq, and tHW, while the "Other H'' category includes ggH, VBF, WH, and ZH. The nonresonant background histograms are stacked, while the two signal, "Other H'', and "top + H'' distributions are shown separately. Boundaries defining event categories are indicated with dotted lines in the upper panel. Events in the grey shaded region are not considered in the analysis. The lower panel shows the ratio of the data to the sum of the nonresonant background predictions. The simulated signal and background distributions are normalized to the integrated luminosity of the data, assuming a coupling of unity for the signal. Statistical and total (statistical $\oplus $ systematic) background uncertainties are represented by the grey- and red-shaded bands, respectively. The (\gamma) + jets sample of multijet and {\gamma + \text {jets}} events from data is not assigned a systematic uncertainty, as described in the text. |
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Figure 2-b:
Hadronic event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions from requirements placed on BDT-nonres (horizontal dotted lines) and BDT-res (vertical dotted lines). The color denotes the $s/\sqrt {b}$ of each category. |
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Figure 3:
The diphoton invariant mass distribution for the selected events from data (black points), and the results of the fits to the signal plus background models (solid red curve), and the background model alone (dotted blue curve), for the categories targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions (left) and ${\mathrm{t} \to \mathrm{H} \mathrm{c}}$ FCNC interactions (right). The signal model is normalized to the best-fit value. The green and yellow bands give the $ \pm $1 and $ \pm $2 standard deviation uncertainties in the background model (dotted blue curve). The background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. Events are weighted by the S/(S+B) of their respective categories. The lower panels show the same information, but with the background component subtracted. |
png pdf |
Figure 3-a:
The diphoton invariant mass distribution for the selected events from data (black points), and the results of the fits to the signal plus background models (solid red curve), and the background model alone (dotted blue curve), for the categories targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions. The signal model is normalized to the best-fit value. The green and yellow bands give the $ \pm $1 and $ \pm $2 standard deviation uncertainties in the background model (dotted blue curve). The background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. Events are weighted by the S/(S+B) of their respective categories. The lower panel shows the same information, but with the background component subtracted. |
png pdf |
Figure 3-b:
The diphoton invariant mass distribution for the selected events from data (black points), and the results of the fits to the signal plus background models (solid red curve), and the background model alone (dotted blue curve), for the categories targeting ${\mathrm{t} \to \mathrm{H} \mathrm{c}}$ FCNC interactions. The signal model is normalized to the best-fit value. The green and yellow bands give the $ \pm $1 and $ \pm $2 standard deviation uncertainties in the background model (dotted blue curve). The background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. Events are weighted by the S/(S+B) of their respective categories. The lower panel shows the same information, but with the background component subtracted. |
png pdf |
Figure 4:
The observed (solid line) and expected (dotted line) 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{u})}$ (left) and ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{c})}$ (right) for each of the hadronic and leptonic categories, defined as described in the text. The last bin gives the overall combined upper limit. The $ \pm $1 and $ \pm$2 standard deviation variations on the expected limit are given by the green and yellow bands, respectively. |
png pdf |
Figure 4-a:
The observed (solid line) and expected (dotted line) 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{u})}$ for each of the hadronic and leptonic categories, defined as described in the text. The last bin gives the overall combined upper limit. The $ \pm $1 and $ \pm$2 standard deviation variations on the expected limit are given by the green and yellow bands, respectively. |
png pdf |
Figure 4-b:
The observed (solid line) and expected (dotted line) 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{c})}$ for each of the hadronic and leptonic categories, defined as described in the text. The last bin gives the overall combined upper limit. The $ \pm $1 and $ \pm$2 standard deviation variations on the expected limit are given by the green and yellow bands, respectively. |
| Summary |
| In summary, we have presented a search for flavor-changing neutral current interactions of the top quark (t) and Higgs boson (H) in proton-proton collisions at a center-of-mass energy of 13 TeV. The processes considered include both the associated production of a single top quark with a Higgs boson via an up or charm quark, and the decay of a top quark to a Higgs boson and an up or charm quark in $\mathrm{t\bar{t}}$ production. No significant excess above the background prediction is observed. The observed (expected) 95% confidence level upper limits on $\mathcal B(\mathrm{t} \to \mathrm{H}\mathrm{u})$ and $\mathcal B(\mathrm{t} \to \mathrm{H}\mathrm{c})$ of 0.019 (0.031)% and 0.073 (0.051)%, respectively, are the most stringent experimental limits published to date. |
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