CMS-PAS-TOP-21-007

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.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right).
png pdf	Figure 1-a: Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right).
png pdf	Figure 1-b: Leading diagrams for ${\mathrm{t} {}\mathrm{\bar{t}}}$ central exclusive production, via $\gamma {}\gamma$ fusion (left) and pomeron exchange (right).
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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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