Measurement of the Top Pair Production Cross Section at sqrt(s)=7 TeV using b-quark Jet Identification Techniques in Lepton + Jet Events

Abstract

An updated measurement of the production cross section for pp → ttbar at a center-of-mass energy of 7 TeV using data collected by the CMS detector at the Large Hadron Collider is presented. The analysis uses data corresponding to an integrated luminosity between 804-1087 pb-1 using events with one isolated, high transverse momentum muon or electron, large missing transverse energy and hadronic jets. The ttbar content of the data has been enhanced by requiring the presence of at least one jet consistent with originating from a b-quark. The measured cross section is 164.4 ± 2.8 (stat.) ±11.9 (syst.) ± 7.4 (lum.)pb and is consistent with higher order QCD calculations.

Approved results from TOP-11-003 (click on result to get .pdf)

Result Channel
Fitted ttbar cross section for the electron+jets channel PDF
Fitted ttbar cross section for the muon+jets channel PDF
Fitted ttbar cross section for the combined electron+jets and muon+jets channel PDF

Approved plots and tables (click on image to get .png)

Figure Abbreviated caption
SHYFT_legend.png Figure 2: legend for profile likelihood plots PDF
tagged_both_svm_1j_1t_mu_svm_2j_1t_mu_svm_3j_1t_mu_svm_4j_1t_mu_svm_5j_1t_mu.png Figure 2: combined e+mu fit, muons, 1 b-tag PDF
tagged_both_svm_1j_1t_el_svm_2j_1t_el_svm_3j_1t_el_svm_4j_1t_el_svm_5j_1t_el.png Figure 2: combined e+mu fit, electrons, 1 b-tag PDF
tagged_both_svm_2j_2t_mu_svm_3j_2t_mu_svm_4j_2t_mu_svm_5j_2t_mu.png Figure 2: combined e+mu fit, muons, >=2 b-tag PDF
tagged_both_svm_2j_2t_el_svm_3j_2t_el_svm_4j_2t_el_svm_5j_2t_el.png Figure 2: combined e+mu fit, electrons, >=2 b-tag PDF
Table 1: Fitter inputs PDF
Table 2: muon only fit: event counts PDF
Table 3: Systematic uncertainties for the combined e+mu fit, the electron only fit, and the muon only fit. Note: The total is not supposed to be equal to the sum in quadrature of the individual lines. PDF
Table 4: electron only fit: event counts PDF
Table 5: Combined e+mu fit: correlation matrix PDF
Figure 3: (e+jets) Missing transverse energy for events with at least 3 jets and at least 1 btag (pdf)
Figure 3: (e+jets) W transverse Mass for events with at least 3 jets and at least 1 btag(pdf)
Figure 3: (e+jets) Secondary vertex mass for events with at least 3 jets and at least 1 btag(pdf)
Figure 3: (e+jets) HT for events with at least 3 jets and at least 1 btag(pdf)
Figure 3: (e+jets) Lepton pT for events with at least 3 jets and at least 1 btag(pdf)
Figure 3: (e+jets) Lepton eta for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) Missing transverse energy for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) W transverse mass for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) Secondary vertex mass for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) HT for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) Lepton pT for events with at least 3 jets and at least 1 btag(pdf)
Figure 4: (mu+jets) Lepton eta for events with at least 3 jets and at least 1 btag(pdf)

Approved results from TOP-11-003 (cross-check analysis) (click on result to get .pdf)

The cross-check analysis measures the top quark pair cross section using a template fit with 1 b-tag applied in the event selection. To obtain the cross-section from the fit the b-tagging efficiency -which is simultaneously measured- is plugged in introducing a correlation between the two variables. This can be seen from the delta chi2 distribution below. The b tagging efficiency is measured by constructing a b depleted and a b enriched subsample after event selection. The definition of these samples is based on the invariant mass of the b-jet candidate and muon system. The b tagging distribution in the b depleted region is subtracted from the distribution in the b enriched region, resulting in the true b jet b tagging discriminant distribution. The b depleted subsample is normalized to obtain the same non-b jet yield as in the b enriched subsample. The normalisation factor is obtained in a data-driven way.
Result
XSResult_CrossCheck.png cross section in muon+jets PDF
XSResult_CrossCheck.png b tagging efficiency in muon+jets PDF

Figure Abbreviated caption
cross-contour.png Figure 5: delta chi2 distribution PDF
cross-stack.png Figure 5: Invariant mass distribution of the bjet candidate and the muon PDF

-- AmandaDeisher - 21-Sep-2011

Topic attachments
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PDFpdf BtagEff_CrossCheck.pdf r1 manage 27.6 K 2011-09-22 - 11:30 MichaelMaes  
PNGpng BtagEff_CrossCheck.png r1 manage 5.1 K 2011-09-22 - 11:30 MichaelMaes  
PDFpdf SHYFT_legend.pdf r1 manage 155.7 K 2011-09-21 - 16:34 UnknownUser  
PNGpng SHYFT_legend.png r1 manage 14.0 K 2011-09-21 - 16:34 UnknownUser  
PDFpdf XSResult_CrossCheck.pdf r1 manage 122.8 K 2011-09-22 - 11:24 MichaelMaes  
PNGpng XSResult_CrossCheck.png r1 manage 22.8 K 2011-09-22 - 11:24 MichaelMaes  
PDFpdf combinedCorrelationMatrix.pdf r1 manage 17.8 K 2011-09-22 - 15:17 UnknownUser  
PNGpng combinedCorrelationMatrix.png r1 manage 70.8 K 2011-09-22 - 15:03 UnknownUser  
PDFpdf combinedResult.pdf r2 r1 manage 54.6 K 2011-09-21 - 17:22 UnknownUser  
PNGpng combinedResult.png r2 r1 manage 13.8 K 2011-09-21 - 17:22 UnknownUser  
PDFpdf cross-contour.pdf r1 manage 392.9 K 2011-09-22 - 21:43 AndrewMelo cross check contour plot pdf version
PNGpng cross-contour.png r1 manage 22.6 K 2011-09-22 - 21:43 AndrewMelo cross check 2d plot
PDFpdf cross-stack.pdf r2 r1 manage 20.9 K 2011-09-23 - 18:44 AndrewMelo  
PNGpng cross-stack.png r2 r1 manage 13.2 K 2011-09-23 - 18:45 AndrewMelo  
PDFpdf ele_eta.pdf r1 manage 17.0 K 2011-09-23 - 11:42 UnknownUser  
PNGpng ele_eta.png r1 manage 15.9 K 2011-09-23 - 11:42 UnknownUser  
PDFpdf electronOnlyCounts.pdf r5 r4 r3 r2 r1 manage 25.6 K 2011-09-24 - 11:45 SadiaKhalil  
PNGpng electronOnlyCounts.png r5 r4 r3 r2 r1 manage 104.1 K 2011-09-24 - 11:45 SadiaKhalil  
PDFpdf electronOnlyResult.pdf r1 manage 54.6 K 2011-09-21 - 17:14 UnknownUser  
PNGpng electronOnlyResult.png r1 manage 13.7 K 2011-09-21 - 17:13 UnknownUser  
PDFpdf inputs.pdf r1 manage 58.0 K 2011-09-23 - 09:46 UnknownUser  
PNGpng inputs.png r1 manage 42.7 K 2011-09-23 - 09:45 UnknownUser  
PDFpdf mu_eta.pdf r1 manage 16.4 K 2011-09-23 - 11:41 UnknownUser  
PNGpng mu_eta.png r1 manage 15.3 K 2011-09-23 - 11:41 UnknownUser  
PDFpdf muonOnlyCounts.pdf r2 r1 manage 37.1 K 2011-09-24 - 10:37 SadiaKhalil  
PNGpng muonOnlyCounts.png r2 r1 manage 80.0 K 2011-09-24 - 10:38 SadiaKhalil  
PDFpdf muonOnlyResult.pdf r1 manage 54.4 K 2011-09-21 - 17:13 UnknownUser  
PNGpng muonOnlyResult.png r1 manage 13.8 K 2011-09-21 - 17:13 UnknownUser  
PDFpdf pretty_legend.pdf r1 manage 8.3 K 2011-09-22 - 22:58 AndrewMelo Horizontal legend to save space
PDFpdf systAll.pdf r3 r2 r1 manage 38.9 K 2011-09-22 - 15:24 UnknownUser  
PNGpng systAll.png r5 r4 r3 r2 r1 manage 55.4 K 2011-09-22 - 15:23 UnknownUser  
PDFpdf tagged_both_svm_1j_1t_el_svm_2j_1t_el_svm_3j_1t_el_svm_4j_1t_el_svm_5j_1t_el.pdf r3 r2 r1 manage 20.1 K 2011-09-23 - 17:49 MikhailMakouski  
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PDFpdf tagged_both_svm_1j_1t_mu_svm_2j_1t_mu_svm_3j_1t_mu_svm_4j_1t_mu_svm_5j_1t_mu.pdf r3 r2 r1 manage 20.4 K 2011-09-23 - 17:52 MikhailMakouski  
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Topic revision: r27 - 2012-02-08 - RobertoTenchini
 
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