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| CMS-PAS-TOP-16-018 | ||
| Measurement of the differential $\mathrm{t\bar{t}}$ cross section with high-$p_{\mathrm{T}}$ top-quark jets in the all-hadronic channel at $\sqrt{s}= $ 8 TeV | ||
| CMS Collaboration | ||
| August 2017 | ||
| Abstract: A measurement of the differential $\mathrm{t\bar{t}}$ production cross section using 19.7 fb$^{-1}$ of all-jet events with high-$p_\mathrm{T}$ top-quark jets collected by the CMS detector at $\sqrt{s} = $ 8 TeV is presented. This measurement focuses on events where both top quarks decay hadronically, giving rise to a dijet topology. Techniques based on jet substructure are used to suppress standard model backgrounds dominated by QCD multijet production. The remaining background is estimated from data. The $\mathrm{t\bar{t}}$ event yield is extracted in bins of the measured leading top-quark $p_\mathrm{T}$ using a likelihood fit of the invariant mass distribution of top-quark jet candidates. After correcting to parton level, the measured cross section as a function of the leading top-quark $p_\mathrm{T}$ is found to be in agreement with the NLO calculations. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Prefit results of leading jet mass for $ p_{\mathrm{T}} > $ 500 GeV for (left) 0 subjet b tags, (right) 1 subjet b tag, and (center) 2 or more subjet b tags. |
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Figure 1-a:
Prefit results of leading jet mass for $ p_{\mathrm{T}} > $ 500 GeV for 0 subjet b tags. |
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Figure 1-b:
Prefit results of leading jet mass for $ p_{\mathrm{T}} > $ 500 GeV for 1 subjet b tag. |
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Figure 1-c:
Prefit results of leading jet mass for $ p_{\mathrm{T}} > $ 500 GeV for 2 or more subjet b tags. |
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Figure 2:
Postfit results of leading jet mass for (left) 500 $ < p_{\mathrm{T}} < $ 600 and (right) 600 $ < p_{\mathrm{T}} < $ 700 GeV for (from top to bottom) 0 subjet b tags, 1 subjet b tag, 2 or more subjet b tags. |
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Figure 2-a:
Postfit results of leading jet mass for 500 $ < p_{\mathrm{T}} < $ 600 GeV for 0 subjet b tags. |
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Figure 2-b:
Postfit results of leading jet mass for 600 $ < p_{\mathrm{T}} < $ 700 GeV for 0 subjet b tags. |
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Figure 2-c:
Postfit results of leading jet mass for 500 $ < p_{\mathrm{T}} < $ 600 GeV for 1 subjet b tag. |
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Figure 2-d:
Postfit results of leading jet mass for 600 $ < p_{\mathrm{T}} < $ 700 GeV for 1 subjet b tag. |
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Figure 2-e:
Postfit results of leading jet mass for 500 $ < p_{\mathrm{T}} < $ 600 GeV for 2 or more subjet b tags. |
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Figure 2-f:
Postfit results of leading jet mass for 600 $ < p_{\mathrm{T}} < $ 700 GeV for 2 or more subjet b tags. |
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Figure 3:
Postfit results of leading jet mass for (left) 700 $ < p_{\mathrm{T}} < $ 800 and (right) 800 $ < p_{\mathrm{T}} < $ 1200 GeV for (from top to bottom) 0 subjet b tags, 1 subjet b tag, 2 or more subjet b tags. |
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Figure 3-a:
Postfit results of leading jet mass for 700 $ < p_{\mathrm{T}} < $ 800 GeV for 0 subjet b tags. |
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Figure 3-b:
Postfit results of leading jet mass for 800 $ < p_{\mathrm{T}} < $ 1200 GeV for 0 subjet b tags. |
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Figure 3-c:
Postfit results of leading jet mass for 700 $ < p_{\mathrm{T}} < $ 800 GeV for 1 subjet b tag. |
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Figure 3-d:
Postfit results of leading jet mass for 800 $ < p_{\mathrm{T}} < $ 1200 GeV for 1 subjet b tag. |
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Figure 3-e:
Postfit results of leading jet mass for 700 $ < p_{\mathrm{T}} < $ 800 GeV for 2 or more subjet b tags. |
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Figure 3-f:
Postfit results of leading jet mass for 800 $ < p_{\mathrm{T}} < $ 1200 GeV for 2 or more subjet b tags. |
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Figure 4:
Uncertainty due to systematic effects on the unfolded result. |
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Figure 5:
Parton-level differential ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ cross section. |
| Tables | |
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Table 1:
Differential ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ cross section as a function of $ {p_{\mathrm {T}}}$ ($\mathrm{d}\sigma / \mathrm{d} {p_{\mathrm {T}}} $) [fb GeV$ ^{-1}$] unfolded to parton-level with uncertainty. The Data column is the result of this analysis. The uncertainty is divided into Statistical, Experimental, Theoretical, and Total as described in Section \ref {sec:Systematics}. |
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Table 2:
Differential ${\mathrm{ t } {}\mathrm{ \bar{t} } } $ cross section as a function of $ {p_{\mathrm {T}}} (\frac {d\sigma }{d {p_{\mathrm {T}}} }) [\rm fb GeV ^{-1}]$ unfolded to parton-level with uncertainty. This is compared against three generator and parton-shower combinations: POWHEG & PYTHIA 6, mc@nlo & HERWIG++ , and MadGraph & PYTHIA 6 as well as the Semileptonic result from CMS and the NNLO result for CT14 [35]. |
| Summary |
|
A measurement of the differential $\mathrm{ t \bar{t} }$ cross section in the highly boosted all-hadronic channel at $\sqrt{s} = $ 8 TeV at the LHC has been presented. The non-top-quark multijet background is estimated from data, using a procedure which takes into account the fact that the two of the primary discriminants of signal from background, $\tau_{32}$, and jet mass, are correlated. The Alphabet method is used to create a data-driven background in the presence of a correlation with $\tau_{32}$. Data-to-simulation correction factors for N-subjettiness and subjet b-tagging of 0.841 $\pm$ 0.051 and 1.048 $\pm$ 0.070, respectively, are measured. A fit of data and expected signal and background contributions is performed in bins of subjet b tags and jet $p_{\mathrm{T}}$ including systematics. The results of the fits are unfolded using the singular value decomposition method. The results are found to be in agreement with NLO+PS simulation calculations within the large experimental uncertainties. The inclusive integrated $\mathrm{ t \bar{t} }$ cross section for jets with $p_{\mathrm{T}} > $ 500 GeV is also measured, and the result of $\sigma_{\mathrm{ t \bar{t} }} = $ 404 $\pm$ 23 (stat) $\pm$ 25 (exp) $\pm$ 140 (theory) fb agrees more closely with the MC prediction than the POWHEG expectation, but agrees with either within uncertainties. |
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