# TOP-12-023 Measurement of jet multiplicity in di-leptonic top pair events

## Abstract

Jet multiplicity distributions are measured in pp-collisions at sqrt{s} = 7 TeV with the CMS detector using a dataset recorded in 2011 corresponding to an integrated luminosity of 5.0 fb-1.The measurement is performed in the dileptonic decay channels (m+m-, e+e- and m+/- e-/+) of the top-antitop quark pairs, with at least two isolated leptons and at least one b-jet in the final state. The differential top anti-top quark cross section is measured as a function of the jet multiplicity. Furthermore, the distribution of the fraction of events without additional jets above a threshold is measured as functions of the jet transverse momentum and of the scalar sum of the transverse momenta of all additional jets. Several QCD calculations are compared with the data.

## Figures

### Jet multiplicity and kinematic distributions of the additional jets after event selection

Figure Caption
Reconstructed jet multiplicity distribution in the event after event selection for all jets with transverse momenta of at least 30~GeV. The ttbar sample is simulated using MADGRAPH. "ttbar signal" refers to the events decaying dileptonically, "ttbar other" refers to the rest of the decay modes, including \ttbar decays intro prompt tau-leptons. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. [Get pdf version]
Reconstructed jet multiplicity distribution in the event after event selection for all jets with transverse momenta of at least 60 GeV. The \ttbar\ sample is simulated using \MADGRAPH. "\ttbar signal" refers to the events decaying dileptonically, "\ttbar other" refers to the rest of the decay modes, including \ttbar decays intro prompt $\tau$-leptons. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. Notice that the event selection requires two jets with pt>30~GeV. [Get pdf version]
Distribution of the transverse momentum of the first leading additional reconstructed jets compared to signal and background simulated samples. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. [Get pdf version]
Distribution of eta of the first leading additional reconstructed jets compared to signal and background simulated samples. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. [Get pdf version]
Distribution of the transverse momentum of the second leading additional reconstructed jets compared to signal and background simulated samples. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. [Get pdf version]
Distribution of eta of the second leading additional reconstructed jets compared to signal and background simulated samples. The hatched area represents the uncertainty on the predicted \ttbar\ cross section and the luminosity. [Get pdf version]

### Normalised differential cross sections as a function of jet multiplicity

Figure Caption
Normalised differential cross-section as a function of jet multiplicity for jets with pT>30GeV. The data are compared with predictions from MADGRAPH+Pythia, MCATNLO+Herwig and POWHEG+Pythia. The errors on the data points indicate the statistical (inner bars) and the total uncertainty. [Get pdf version]
Normalised differential cross-section as a function of jet multiplicity for jets with pT>30GeV. The figures show the behaviour of MADGRAPH generator when varying the $Q^2$ and matching scales. The errors on the data points indicate the statistical (inner bars) and the total uncertainty. [Get pdf version]
Normalised differential cross-section as a function of jet multiplicity for jets with pT>60GeV. The data are compared with predictions from MADGRAPH+Pythia, MCATNLO+Herwig and POWHEG+Pythia. The errors on the data points indicate the statistical (inner bars) and the total uncertainty. [Get pdf version]
Normalised differential cross-section as a function of jet multiplicity for jets with pT>60GeV. The figures show the behaviour of MADGRAPH generator when varying the $Q^2$ and matching scales. The errors on the data points indicate the statistical (inner bars) and the total uncertainty. [Get pdf version]

### "Gap fraction"

Figure Caption
Measured gap fraction as a function of the additional jet pt. Data are compared to predictions from MADGRAPH+Pythia, POWHEG+Pythia and MC@NLO+Herwig. The errors on the data points indicate the statistical uncertainty. The shaded band corresponds to the statistical and systematic uncertainties (background contamination, PU, b-tagging, JES, JER, unfolding) added in quadrature. [Get pdf version]
Measured gap fraction as a function of the additional jet pt. Data are compared to predictions from MADGRAPH+Pythia and MADGRAPH with varied Q2 and jet-parton matching scales. The errors on the data points indicate the statistical uncertainty. The shaded band corresponds to the statistical and systematic uncertainties (background contamination, PU, b-tagging, JES, JER, unfolding) added in quadrature. [Get pdf version]
Measured gap fraction as a function of the scalar sum of the pt of the additional jets. Data are compared to predictions from MADGRAPH+Pythia, POWHEG+Pythia and MC@NLO+Herwig. The shaded band corresponds to the statistical and systematic uncertainties (background contamination, PU, b-tagging, JES, JER, unfolding) added in quadrature.[Get pdf version]
Measured gap fraction as a function of the scalar sum of the pt of the additional jets. Data are compared to predictions from the nominal MADGRAPH+Pythia and to MADGRAPH with varied Q2 and jet-parton matching scales. The errors on the data points indicate the statistical uncertainty. The shaded band corresponds to the statistical and systematic uncertainties (background contamination, PU, b-tagging, JES, JER, unfolding) added in quadrature. [Get pdf version]

### Public Supplemental material

-- CarmenDiezPardos - 14-Sep-2012

Topic attachments
I Attachment History Action Size Date Who Comment
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png HypExtraJetEta2.png r2 r1 manage 20.1 K 2012-09-14 - 20:16 CarmenDiezPardos
pdf HypExtraJetpT.pdf r1 manage 25.7 K 2012-09-14 - 10:42 CarmenDiezPardos
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pdf HypExtraJetpT2.pdf r1 manage 22.7 K 2012-09-14 - 10:42 CarmenDiezPardos
png HypExtraJetpT2.png r2 r1 manage 20.5 K 2012-09-14 - 20:16 CarmenDiezPardos
pdf HypJetMult.pdf r1 manage 18.0 K 2012-09-14 - 12:27 CarmenDiezPardos
png HypJetMult.png r2 r1 manage 18.5 K 2012-09-14 - 20:16 CarmenDiezPardos
pdf HypJetMultpt60.pdf r1 manage 17.9 K 2012-09-14 - 12:27 CarmenDiezPardos
png HypJetMultpt60.png r2 r1 manage 18.5 K 2012-09-14 - 20:16 CarmenDiezPardos
Topic revision: r8 - 2013-04-11 - RobertoTenchini

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