# Measurement of the top quark-antiquark pair production in association with a W or Z boson in pp collisions at = 8 TeV

### Abstract

A measurement of the cross section for the production of top quark-antiquark pairs () in association with a vector boson (W or Z) in proton-proton collisions at = 8TeV is presented. The results are based on a dataset corresponding to an integrated luminosity of recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and ) channels: a same-sign dilepton analysis targeting events, and trilepton and four-lepton analyses designed for events. In the same-sign dilepton channel, the W cross section is measured as with a significance of 1.6 standard deviations. Combining the trilepton and four-lepton channels, a direct measurement of the Z cross section, , is obtained with a significance of 3.2 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive process, where V stands for W or Z, is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.

### Introduction

Figure (left) Figure (right) Caption
The dominant leading-order Feynman diagrams for ttW and ttZ production in pp collisions. The charge conjugate of the diagrams shown is implied.

### Same-sign dilepton analysis

Figure (left) Figure (right) Caption
Event yields in data after final dilepton selection requirements, compared to the background estimates and signal expectations. Contributions separated by final states (left) and trijets mass distribution for the hadronic top-quark candidate (right).The combination of statistical and systematic uncertainties is denoted by the shaded area.
Event yields in data after final dilepton selection requirements, compared to the background estimates and signal expectations. HT distribution (left) and the leading-lepton distribution (right). The combination of statistical and systematic uncertainties is denoted by the shaded area.

Table Caption
Estimated backgrounds, expected signal, and observed number of events for the , , and channels. Uncertainties include both the statistical and the systematic components.The systematic uncertainty in the signal contribution does not include the theoretical uncertainty in the signal production cross section.

### Trilepton analysis

Figure (left) Figure (right) Caption
Event yields in data after final trilepton selection requirements, compared to the background estimates and signal expectations. Contributions separated by final states where the two leptons consistent with the Z boson are inside parenthesis on the bin labels (left) and trijets mass distribution for the hadronic top-quark candidate (right). The combination of statistical and systematic uncertainties is denoted by the shaded area.
Event yields in data after final trilepton selection requirements, compared to the background estimates and signal expectations. Z-boson candidate dilepton mass distribution (left) and the distribution of the number of b-tagged jets passing medium operating point of the b-tagger (right). The combination of statistical and systematic uncertainties is denoted by the shaded area.

Table Caption
Estimated backgrounds, expected signal, and observed number of events for the trilepton channel. Uncertainties include both the statistical and the systematic components.The systematic uncertainty in the signal contribution does not include the theoretical uncertainty in the signal production cross section.

### Four-lepton analysis

Figure (left) Figure (right) Caption
Event yields in data after final four-lepton selection requirements, compared to the background estimates and signal expectations. Contributions in the 1~b-tagged jet and 2~b-tagged jets signal regions (left) and inclusive MET distribution (right). The ZZ component of the background is shown separately from the rest of the irreducible processes. The combination of statistical and systematic uncertainties is denoted by the shaded area.

Table Caption
Estimated backgrounds, expected signal, and observed number of events for the four-lepton channel. Uncertainties include both the statistical and the systematic components. The systematic uncertainty in the signal contribution does not include the theoretical uncertainty in the signal production cross section. The ZZ component of the background is shown separately from the rest of the irreducible processes.

### Systematic uncertainties in signal selection efficiency

Table Caption
Systematic uncertainties in the signal selection efficiency for the three considered channels: ttW in dilepton (2) final state; ttZ in trilepton (3) and four-lepton (4) final states.

### Results

Table/Figure Caption
Results of the extraction of cross sections, from single and combined channels.
Results for the two dimensional fit of the ttW and ttZ cross sections.
The result of the two-dimensional best fit for ttW and ttZ cross sections (cross symbol) is shown along with its 68 and 95% confidence level contours. The result of this fit is superimposed with the separate ttW and ttZ cross-section measurements, and the corresponding bands, obtained from the dilepton, and the trilepton/four-lepton channels, respectively. The figure also shows the predictions from theory and the corresponding uncertainties.

Topic attachments
I Attachment History Action Size Date Who Comment
pdf ObsPred_FinalSel_ALL_HT_preliminary.pdf r1 manage 16.0 K 2014-05-30 - 23:16 BorisMangano
png ObsPred_FinalSel_ALL_HT_preliminary.png r1 manage 309.9 K 2014-05-30 - 23:16 BorisMangano
pdf ObsPred_FinalSel_ALL_M3_preliminary.pdf r1 manage 16.5 K 2014-05-30 - 23:16 BorisMangano
png ObsPred_FinalSel_ALL_M3_preliminary.png r1 manage 308.9 K 2014-05-30 - 23:16 BorisMangano
pdf ObsPred_FinalSel_ALL_pT1_preliminary.pdf r1 manage 16.1 K 2014-05-30 - 23:16 BorisMangano
png ObsPred_FinalSel_ALL_pT1_preliminary.png r1 manage 315.3 K 2014-05-30 - 23:16 BorisMangano
pdf ObsPred_pp_mm_TotalBin_preliminary.pdf r1 manage 32.5 K 2014-05-30 - 23:17 BorisMangano
png ObsPred_pp_mm_TotalBin_preliminary.png r1 manage 269.3 K 2014-05-30 - 23:17 BorisMangano
pdf comb1.pdf r1 manage 106.0 K 2014-05-30 - 23:48 BorisMangano
png comb1.png r1 manage 75.3 K 2014-05-30 - 23:48 BorisMangano
pdf comb2.pdf r1 manage 106.0 K 2014-05-30 - 23:48 BorisMangano
png comb2.png r1 manage 31.1 K 2014-05-30 - 23:48 BorisMangano
pdf figure_MET_PRELIMINARY.pdf r1 manage 11.8 K 2014-05-30 - 23:17 BorisMangano
png figure_MET_PRELIMINARY.png r1 manage 284.8 K 2014-05-30 - 23:17 BorisMangano
pdf figure_PRELIMINARY.pdf r1 manage 11.0 K 2014-05-30 - 23:17 BorisMangano
png figure_PRELIMINARY.png r1 manage 240.2 K 2014-05-30 - 23:17 BorisMangano
pdf fit_2d.pdf r2 r1 manage 55.8 K 2014-05-31 - 00:02 BorisMangano
png fit_2d.png r2 r1 manage 318.7 K 2014-05-31 - 00:02 BorisMangano
pdf hNMedium_3L2J2b_preliminary.pdf r1 manage 14.8 K 2014-05-30 - 23:17 BorisMangano
png hNMedium_3L2J2b_preliminary.png r1 manage 16.0 K 2014-05-30 - 23:17 BorisMangano
pdf hTopMass_3L2J2b_preliminary.pdf r1 manage 15.7 K 2014-05-30 - 23:17 BorisMangano
png hTopMass_3L2J2b_preliminary.png r1 manage 16.7 K 2014-05-30 - 23:17 BorisMangano
pdf hYields_3L2J2b_preliminary.pdf r1 manage 14.8 K 2014-05-30 - 23:17 BorisMangano
png hYields_3L2J2b_preliminary.png r1 manage 16.0 K 2014-05-30 - 23:17 BorisMangano
pdf hZMass_3L2J2b_preliminary.pdf r1 manage 15.3 K 2014-05-30 - 23:17 BorisMangano
png hZMass_3L2J2b_preliminary.png r1 manage 16.8 K 2014-05-30 - 23:17 BorisMangano
pdf syst.pdf r1 manage 89.1 K 2014-05-30 - 23:48 BorisMangano
png syst.png r1 manage 107.9 K 2014-05-30 - 23:48 BorisMangano
pdf tab2L.pdf r1 manage 125.9 K 2014-05-30 - 23:48 BorisMangano
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pdf tab3L.pdf r1 manage 110.8 K 2014-05-30 - 23:48 BorisMangano
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pdf tab4L.pdf r1 manage 89.1 K 2014-05-30 - 23:48 BorisMangano
png tab4L.png r1 manage 83.9 K 2014-05-30 - 23:48 BorisMangano
pdf ttW.pdf r1 manage 6.1 K 2014-05-30 - 23:16 BorisMangano
png ttW.png r1 manage 81.7 K 2014-05-30 - 23:16 BorisMangano
pdf ttZ.pdf r1 manage 5.2 K 2014-05-30 - 23:16 BorisMangano
png ttZ.png r1 manage 109.3 K 2014-05-30 - 23:16 BorisMangano
Topic revision: r5 - 2014-06-26 - AndreasMeyer

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