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| CMS-PAS-TOP-21-007 | ||
| Search for central exclusive production of top quark pairs in proton-proton collisions at $\sqrt{s} = $ 13 TeV with tagged protons | ||
| CMS Collaboration | ||
| March 2022 | ||
| Abstract: A search for the central exclusive production of top quark pairs ($\mathrm{t\bar{t}}$) is performed using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb$^{-1}$. The $\mathrm{t\bar{t}}$ decay products are reconstructed using the CMS central detector, while forward protons are detected with the CMS-TOTEM Precision Proton Spectrometer. An upper bound on the production cross section of 0.59\ pb is set at 95% confidence level. | ||
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These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right). |
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Figure 1-a:
Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right). |
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Figure 1-b:
Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right). |
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Figure 2:
A schematic layout of one arm of CT-PPS along the LHC beam line. The RP shown in red are those used by CT-PPS; those in grey are part of the TOTEM experiment. |
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Figure 3:
Normalised distribution of the relative invariant mass resolution of the reconstructed ${\mathrm{t} {}\mathrm{\bar{t}}}$ system for the dilepton (left) and $\ell $+jets (right) analyses. For the $\ell $+jets mode, the hatched blue and dotted red histograms represent the distribution before and after applying the kinematic fit, respectively. |
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Figure 3-a:
Normalised distribution of the relative invariant mass resolution of the reconstructed ${\mathrm{t} {}\mathrm{\bar{t}}}$ system for the dilepton (left) and $\ell $+jets (right) analyses. For the $\ell $+jets mode, the hatched blue and dotted red histograms represent the distribution before and after applying the kinematic fit, respectively. |
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Figure 3-b:
Normalised distribution of the relative invariant mass resolution of the reconstructed ${\mathrm{t} {}\mathrm{\bar{t}}}$ system for the dilepton (left) and $\ell $+jets (right) analyses. For the $\ell $+jets mode, the hatched blue and dotted red histograms represent the distribution before and after applying the kinematic fit, respectively. |
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Figure 4:
Distribution of the proton fractional momentum loss $\xi $ in data and background simulated samples after pileup proton mixing and pileup reweighting, in the $\ell $ + jets channel. Solid histograms: background; open histogram: signal, normalised to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 4-a:
Distribution of the proton fractional momentum loss $\xi $ in data and background simulated samples after pileup proton mixing and pileup reweighting, in the $\ell $ + jets channel. Solid histograms: background; open histogram: signal, normalised to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 4-b:
Distribution of the proton fractional momentum loss $\xi $ in data and background simulated samples after pileup proton mixing and pileup reweighting, in the $\ell $ + jets channel. Solid histograms: background; open histogram: signal, normalised to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-a:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-b:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-c:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-d:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-e:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-f:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-g:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 5-h:
Distribution of some of the kinematic variables of interest for the dilepton (top) and $\ell $+jets (bottom) analysis. Solid histograms: background; open histogram: signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18]; points with error bars: data. |
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Figure 6:
Distribution of the BDT score in the signal region for simulated events after the fit, and for data. Left: dilepton mode; right: $\ell $+jets mode. The red open histogram shows the expected distribution for signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18];. For both reconstruction modes, all signal regions are combined. |
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Figure 6-a:
Distribution of the BDT score in the signal region for simulated events after the fit, and for data. Left: dilepton mode; right: $\ell $+jets mode. The red open histogram shows the expected distribution for signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18];. For both reconstruction modes, all signal regions are combined. |
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Figure 6-b:
Distribution of the BDT score in the signal region for simulated events after the fit, and for data. Left: dilepton mode; right: $\ell $+jets mode. The red open histogram shows the expected distribution for signal, normalized to a cross section of 25 pb, approximately 10$^5$ larger than the SM cross section prediction from [18];. For both reconstruction modes, all signal regions are combined. |
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Figure 7:
Expected 95% CL upper limit for the signal cross section, for the two reconstruction modes and for the combination. The green and yellow bands show the $ \pm $1$ \sigma $ and $ \pm $2$ \sigma $ intervals, respectively. |
| Summary |
| In summary, we have searched for the central exclusive production of top quark-antiquark pairs in proton-proton interactions, ${\mathrm{p}} {\mathrm{p}} \rightarrow {\mathrm{p}} \mathrm{t\bar{t}} {\mathrm{p}}$, for the first time using tagged intact protons, reconstructed by the CMS-TOTEM Precision Proton Spectrometer. The $\mathrm{t\bar{t}}$ pairs are reconstructed by the CMS detector either in the dilepton or the lepton+jets decay modes: the search is conducted separately for the two modes, and the results are combined at the end. With a data sample of proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 29.4 fb$^{-1}$, results consistent with predictions from the standard model are obtained, and an upper limit of 0.59 pb at the 95% confidence level is set on the central exclusive production of $\mathrm{t\bar{t}}$ pairs. |
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