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| CMS-PAS-TOP-20-007 | ||
| Search for flavor-changing neutral current interactions of the top quark and the Higgs boson in the diphoton decay channel in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| June 2021 | ||
| Abstract: Proton-proton interactions resulting in the prodution of a Higgs boson with subsequent decay into two photons are studied in a search for the signature of flavor-changing neutral current interactions of top quarks and Higgs bosons. The analysis is based on data collected at a center-of-mass energy $\sqrt{s}= $ 13 TeV by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. Multivariate machine learning techniques are used to separate signal and standard model background processes. No significant excess above the background prediction is observed, and upper limits on the $\mathrm{t} \to \mathrm{Hq}$ branching fractions are derived through a binned fit to the diphoton invariant mass spectrum. The observed (expected) 95% confidence level upper limits are found to be 1.9 $\times$ 10$^{-4}$ (3.1 $\times$ 10$^{-4}$) for $\mathcal B(\mathrm{t} \to \mathrm{Hu})$ and 7.3 $\times$ 10$^{-4}$ (5.1 $\times$ 10$^{-4}$) for $\mathcal B(\mathrm{t} \to \mathrm{Hc})$. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here. |
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| Figures | |
png pdf |
Figure 1:
Representative Feynman diagrams for the considered FCNC production modes: associated production of a top quark with the Higgs boson (left) and ${\mathrm{t} {}\mathrm{\bar{t}}}$ production with the decay of the top quark to a Higgs boson and an up or charm quark (right). The FCNC vertex in each process is denoted with a red circle. |
png pdf |
Figure 2:
Distributions of BDT-NRB (left) and BDT-SMH (right) output used for the event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions in the hadronic channel. The "Other'' category includes contributions from ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$, ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$, ${\mathrm{W} \mathrm{W}}$, ${\mathrm{W} \mathrm{Z}}$, ${\mathrm{Z} \mathrm{Z}}$, and $\mathrm{t}$ + $\gamma $ + jets. Category boundaries are indicated with dotted lines. Events in the grey shaded region are not considered in the analysis. The lower panels show the ratio of the data to the MC predictions. Statistical and total (statistical $\oplus $ systematic) background uncertainties are represented by the black and red shaded bands, respectively. No systematic uncertainty is considered for the ($\gamma$) + jets sample of events from data. |
png pdf |
Figure 2-a:
Distributions of BDT-NRB (left) and BDT-SMH (right) output used for the event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions in the hadronic channel. The "Other'' category includes contributions from ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$, ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$, ${\mathrm{W} \mathrm{W}}$, ${\mathrm{W} \mathrm{Z}}$, ${\mathrm{Z} \mathrm{Z}}$, and $\mathrm{t}$ + $\gamma $ + jets. Category boundaries are indicated with dotted lines. Events in the grey shaded region are not considered in the analysis. The lower panels show the ratio of the data to the MC predictions. Statistical and total (statistical $\oplus $ systematic) background uncertainties are represented by the black and red shaded bands, respectively. No systematic uncertainty is considered for the ($\gamma$) + jets sample of events from data. |
png pdf |
Figure 2-b:
Distributions of BDT-NRB (left) and BDT-SMH (right) output used for the event categorization targeting ${\mathrm{t} \to \mathrm{H} \mathrm{u}}$ FCNC interactions in the hadronic channel. The "Other'' category includes contributions from ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$, ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$, ${\mathrm{W} \mathrm{W}}$, ${\mathrm{W} \mathrm{Z}}$, ${\mathrm{Z} \mathrm{Z}}$, and $\mathrm{t}$ + $\gamma $ + jets. Category boundaries are indicated with dotted lines. Events in the grey shaded region are not considered in the analysis. The lower panels show the ratio of the data to the MC predictions. Statistical and total (statistical $\oplus $ systematic) background uncertainties are represented by the black and red shaded bands, respectively. No systematic uncertainty is considered for the ($\gamma$) + jets sample of events from data. |
png pdf |
Figure 3:
Invariant mass distribution for the selected events (black points), along with signal and background models 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 expected 95% CL upper limit on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{q})}$. Events are weighted by the $ S / (S + B) $ of their respective categories. Note that the background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. The lower panels show the same information, but with the background model subtracted from each quantity. |
png pdf |
Figure 3-a:
Invariant mass distribution for the selected events (black points), along with signal and background models 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 expected 95% CL upper limit on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{q})}$. Events are weighted by the $ S / (S + B) $ of their respective categories. Note that the background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. The lower panels show the same information, but with the background model subtracted from each quantity. |
png pdf |
Figure 3-b:
Invariant mass distribution for the selected events (black points), along with signal and background models 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 expected 95% CL upper limit on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{q})}$. Events are weighted by the $ S / (S + B) $ of their respective categories. Note that the background model includes ${\mathrm{H} \to \gamma \gamma}$ events from SM processes. The lower panels show the same information, but with the background model subtracted from each quantity. |
png pdf |
Figure 4:
Expected and observed 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{u})}$ vs. ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{c})}$ (left) and $\kappa _{\mathrm{H} \mathrm{u} \mathrm{t}}$ vs. $\kappa _{\mathrm{H} \mathrm{c} \mathrm{t}}$ (right). |
png pdf |
Figure 4-a:
Expected and observed 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{u})}$ vs. ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{c})}$ (left) and $\kappa _{\mathrm{H} \mathrm{u} \mathrm{t}}$ vs. $\kappa _{\mathrm{H} \mathrm{c} \mathrm{t}}$ (right). |
png pdf |
Figure 4-b:
Expected and observed 95% CL upper limits on ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{u})}$ vs. ${\mathcal B(\mathrm{t} \to \mathrm{H} \mathrm{c})}$ (left) and $\kappa _{\mathrm{H} \mathrm{u} \mathrm{t}}$ vs. $\kappa _{\mathrm{H} \mathrm{c} \mathrm{t}}$ (right). |
| Summary |
| In conclusion, we have presented a search for FCNC interactions of the top quark and the Higgs boson, considering both the associated production of a single top quark with a Higgs boson via a light-flavor quark and the decay of a top quark to a Higgs boson and light-flavor quark in ${\mathrm{t} {}\mathrm{\bar{t}}}$ production. No significant excess above the background prediction is observed and limits on the ${\mathrm{t} \to \mathrm{H} \mathrm{q}}$ branching fractions are derived. The observed (expected) 95% CL upper limits on $\mathcal B(\mathrm{t} \to \mathrm{Hu})$ and $\mathcal B(\mathrm{t} \to \mathrm{Hc})$ of 1.9 $\times$ 10$^{-4}$ (3.1 $\times$ 10$^{-4}$) and 7.3 $\times$ 10$^{-4}$ (5.1 $\times$ 10$^{-4}$), respectively. |
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