CMS-PAS-TOP-16-018

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 & Tables	Summary	References	CMS Publications

Figures
png pdf	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.
png	Figure 1-a: Prefit results of leading jet mass for $p_{\mathrm{T}} >$ 500 GeV for 0 subjet b tags.
png	Figure 1-b: Prefit results of leading jet mass for $p_{\mathrm{T}} >$ 500 GeV for 1 subjet b tag.
png	Figure 1-c: Prefit results of leading jet mass for $p_{\mathrm{T}} >$ 500 GeV for 2 or more subjet b tags.
png pdf	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.
png	Figure 2-a: Postfit results of leading jet mass for 500 $< p_{\mathrm{T}} <$ 600 GeV for 0 subjet b tags.
png	Figure 2-b: Postfit results of leading jet mass for 600 $< p_{\mathrm{T}} <$ 700 GeV for 0 subjet b tags.
png	Figure 2-c: Postfit results of leading jet mass for 500 $< p_{\mathrm{T}} <$ 600 GeV for 1 subjet b tag.
png	Figure 2-d: Postfit results of leading jet mass for 600 $< p_{\mathrm{T}} <$ 700 GeV for 1 subjet b tag.
png	Figure 2-e: Postfit results of leading jet mass for 500 $< p_{\mathrm{T}} <$ 600 GeV for 2 or more subjet b tags.
png	Figure 2-f: Postfit results of leading jet mass for 600 $< p_{\mathrm{T}} <$ 700 GeV for 2 or more subjet b tags.
png pdf	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.
png	Figure 3-a: Postfit results of leading jet mass for 700 $< p_{\mathrm{T}} <$ 800 GeV for 0 subjet b tags.
png	Figure 3-b: Postfit results of leading jet mass for 800 $< p_{\mathrm{T}} <$ 1200 GeV for 0 subjet b tags.
png	Figure 3-c: Postfit results of leading jet mass for 700 $< p_{\mathrm{T}} <$ 800 GeV for 1 subjet b tag.
png	Figure 3-d: Postfit results of leading jet mass for 800 $< p_{\mathrm{T}} <$ 1200 GeV for 1 subjet b tag.
png	Figure 3-e: Postfit results of leading jet mass for 700 $< p_{\mathrm{T}} <$ 800 GeV for 2 or more subjet b tags.
png	Figure 3-f: Postfit results of leading jet mass for 800 $< p_{\mathrm{T}} <$ 1200 GeV for 2 or more subjet b tags.
png pdf	Figure 4: Uncertainty due to systematic effects on the unfolded result.
png pdf	Figure 5: Parton-level differential ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ cross section.

Tables
png pdf	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}.
png pdf	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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