TOP-11-005
Measurement of the ttbar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

Abstract

The production cross section ( ) is measured in proton-proton collisions at TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of . The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets categorized through b-tagging criteria and the presence of an imbalance in transverse momentum. For a top-quark mass of 172.5 GeV, the measured value of is consistent with predictions from the standard model.

Cross section and mass of the top quark

The cross section dependence for top-quark masses in the range 160-185 GeV can be parametrized as

Figures

Figures Caption
fig1a.png fig1b.png fig1c.png Figure 1 The distributions for the highest- (a) electrons, (b) muons, and (c) jets, after the jet multiplicity selection. The expected distributions for the signal and individual backgrounds are shown by the histograms, and include all data-based corrections. A cross section of 164 pb is used to normalize the simulated signal. In this and all following figures, the hatched regions show the total uncertainties on the sum of the and background predictions. The ratios of data to the sum of the and background predictions are given at the bottom of each panel. PDF version (a), (b) and (c).
fig2a.png fig2b.png fig2c.png Figure 2 Same as Fig. 1, but for the second-highest pT electrons, muons and jets in each event. PDF version (a), (b) and (c).
fig3a.png fig3b.png Figure 3 Same as Fig.1, but for the dilepton invariant-mass distribution of the (a) emu channel and (b) the sum of the ee and mumu channels. The gap in the latter distribution is due to the requirement that removes dileptons from Z decay. PDF version (a) and (b).
fig4a.png fig4b.png Figure 4 Same as Fig.3, but for the \met\ distributions. PDF version (a) and (b).
fig5a.pngfig5b.png Figure 5 The jet multiplicity for events passing the dilepton and \met\ criteria, but before the b-tagging requirement, for (a) emu and (b) the sum of ee and mumu channels. PDF version for (a)and (b).
fig6a.pngfig6b.png Figure 6 The multiplicity of b-tagged jets in events passing full event selections, for (a) emu and (b) the summed ee and mumu channels. PDF version for (a) and (b).
plotPLR.png The two-dimensional distribution of and , projected onto a single axis representing (), for data and signal plus background sources, combining the decay channels ee, mumu and emu. PDF version plots_PLR.pdf.

Tables

Tables Caption
table1.png Estimated number of W-like () and MJ-like () events before and after b tagging.
table2.png Summary of the relative (\%) systematic uncertainties on the number of signal \ttbar\ events after applying the full selection criteria, before b tagging and with at least 1 b-tagged jet in the event. Combined uncertainties are listed for the sum of contributions from the three dilepton channels, except for lepton efficiencies, which are given separately for ee, mumu and emu events.
table3.png Numbers of dilepton events in the ee, mumu, and emu channels after all the event selection criteria, without requiring a b-tagged jet (top), and requiring at least one b-tagged jet (middle), for different sources: background, \ttbar\ signal for a cross section of 164 pb, and data. The uncertainties shown include the statistical and systematic uncertainties added in quadrature. The lower part of the table gives the \ttbar\ acceptances, including the dilepton branching fraction, from the simulation.
table4.png Summary of the individual contributions to the systematic uncertainty on the measurement for the combined dilepton sample, using the counting method. The uncertainties are given in pb. The statistic uncertainty is also given for comparison.
table5.png Measured $\sigma_{\ttbar}$ in pb ( stat syst lumi) for a top-quark mass of 172.5 GeV, for each of the dilepton channels, as well as for their combination.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf fig1a.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig1a.png r1 manage 43.8 K 2012-06-30 - 17:38 JeremyAndrea fig1A
PDFpdf fig1b.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig1b.png r1 manage 44.4 K 2012-06-30 - 17:40 JeremyAndrea fig1b
PDFpdf fig1c.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig1c.png r1 manage 45.1 K 2012-06-30 - 17:40 JeremyAndrea fig&c
PDFpdf fig2a.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig2a.png r1 manage 39.2 K 2012-06-30 - 17:40 JeremyAndrea fig2a
PDFpdf fig2b.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig2b.png r1 manage 40.3 K 2012-06-30 - 17:41 JeremyAndrea fig2b
PDFpdf fig2c.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig2c.png r1 manage 40.3 K 2012-06-30 - 17:41 JeremyAndrea fig2c
PDFpdf fig3a.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig3a.png r1 manage 44.5 K 2012-06-30 - 17:41 JeremyAndrea fig3a
PDFpdf fig3b.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig3b.png r1 manage 41.3 K 2012-06-30 - 17:42 JeremyAndrea fig3b
PDFpdf fig4a.pdf r1 manage 201.6 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig4a.png r1 manage 42.0 K 2012-06-30 - 17:42 JeremyAndrea fig4a
PDFpdf fig4b.pdf r1 manage 201.6 K 2012-06-30 - 18:09 JeremyAndrea  
PNGpng fig4b.png r1 manage 38.5 K 2012-06-30 - 17:42 JeremyAndrea fig4b
PDFpdf fig5a.pdf r1 manage 201.6 K 2012-06-30 - 18:10 JeremyAndrea  
PNGpng fig5a.png r1 manage 31.1 K 2012-06-30 - 17:42 JeremyAndrea fig5a
PDFpdf fig5b.pdf r1 manage 201.6 K 2012-06-30 - 18:10 JeremyAndrea  
PNGpng fig5b.png r1 manage 31.4 K 2012-06-30 - 17:43 JeremyAndrea fig5b
PDFpdf fig6a.pdf r1 manage 123.3 K 2012-06-30 - 18:10 JeremyAndrea  
PNGpng fig6a.png r1 manage 32.1 K 2012-06-30 - 17:43 JeremyAndrea fig6a
PDFpdf fig6b.pdf r1 manage 123.3 K 2012-06-30 - 18:10 JeremyAndrea  
PNGpng fig6b.png r1 manage 31.0 K 2012-06-30 - 17:43 JeremyAndrea  
PNGpng plotPLR.png r1 manage 38.1 K 2012-06-30 - 17:56 JeremyAndrea  
PDFpdf plots_PLR.pdf r1 manage 16.8 K 2012-06-30 - 18:24 JeremyAndrea  
PNGpng table1.png r1 manage 16.6 K 2012-06-30 - 18:01 JeremyAndrea table1
PNGpng table2.png r1 manage 50.9 K 2012-06-30 - 18:02 JeremyAndrea table2
PNGpng table3.png r1 manage 101.6 K 2012-06-30 - 18:02 JeremyAndrea tables
PNGpng table4.png r1 manage 22.0 K 2012-06-30 - 18:02 JeremyAndrea tables
PNGpng table5.png r1 manage 60.2 K 2012-06-30 - 18:02 JeremyAndrea tables
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Topic revision: r3 - 2012-07-02 - RobertoTenchini
 
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