# 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
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).
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).
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).
Figure 4 Same as Fig.3, but for the \met\ distributions. PDF version (a) and (b).
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).
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).
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
Estimated number of W-like () and MJ-like () events before and after b tagging.
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.
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.
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.
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
pdf fig1a.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea
png fig1a.png r1 manage 43.8 K 2012-06-30 - 17:38 JeremyAndrea fig1A
pdf fig1b.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea
png fig1b.png r1 manage 44.4 K 2012-06-30 - 17:40 JeremyAndrea fig1b
pdf fig1c.pdf r1 manage 200.8 K 2012-06-30 - 18:09 JeremyAndrea
png fig1c.png r1 manage 45.1 K 2012-06-30 - 17:40 JeremyAndrea fig&c
pdf fig2a.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea
png fig2a.png r1 manage 39.2 K 2012-06-30 - 17:40 JeremyAndrea fig2a
pdf fig2b.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea
png fig2b.png r1 manage 40.3 K 2012-06-30 - 17:41 JeremyAndrea fig2b
pdf fig2c.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea
png fig2c.png r1 manage 40.3 K 2012-06-30 - 17:41 JeremyAndrea fig2c
pdf fig3a.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea
png fig3a.png r1 manage 44.5 K 2012-06-30 - 17:41 JeremyAndrea fig3a
pdf fig3b.pdf r1 manage 272.4 K 2012-06-30 - 18:09 JeremyAndrea
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pdf fig4a.pdf r1 manage 201.6 K 2012-06-30 - 18:09 JeremyAndrea
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pdf fig4b.pdf r1 manage 201.6 K 2012-06-30 - 18:09 JeremyAndrea
png fig4b.png r1 manage 38.5 K 2012-06-30 - 17:42 JeremyAndrea fig4b
pdf fig5a.pdf r1 manage 201.6 K 2012-06-30 - 18:10 JeremyAndrea
png fig5a.png r1 manage 31.1 K 2012-06-30 - 17:42 JeremyAndrea fig5a
pdf fig5b.pdf r1 manage 201.6 K 2012-06-30 - 18:10 JeremyAndrea
png fig5b.png r1 manage 31.4 K 2012-06-30 - 17:43 JeremyAndrea fig5b
pdf fig6a.pdf r1 manage 123.3 K 2012-06-30 - 18:10 JeremyAndrea
png fig6a.png r1 manage 32.1 K 2012-06-30 - 17:43 JeremyAndrea fig6a
pdf fig6b.pdf r1 manage 123.3 K 2012-06-30 - 18:10 JeremyAndrea
png fig6b.png r1 manage 31.0 K 2012-06-30 - 17:43 JeremyAndrea
png plotPLR.png r1 manage 38.1 K 2012-06-30 - 17:56 JeremyAndrea
pdf plots_PLR.pdf r1 manage 16.8 K 2012-06-30 - 18:24 JeremyAndrea
png table1.png r1 manage 16.6 K 2012-06-30 - 18:01 JeremyAndrea table1
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Topic revision: r3 - 2012-07-02 - RobertoTenchini

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