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| CMS-PAS-TOP-17-005 | ||
| Measurement of top quark pair-production in association with a W or Z boson in pp collisions at 13 TeV | ||
| CMS Collaboration | ||
| May 2017 | ||
| Abstract: We present a measurement of the cross section of top quark pair production in association with a W or Z boson, in proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. The data sample used corresponds to an integrated luminosity of 35.9 fb−1, collected in 2016 by the CMS experiment. The measurement is performed in same-charge dilepton, three- and four-lepton final states where the jet and b-jet multiplicities are exploited to enhance the signal-to-background ratio. The t¯tW and t¯tZ production cross sections are measured to be σ(t¯tW)= 0.80+0.12−0.11 (stat.) +0.13−0.12 (sys.) pb and σ(t¯tZ)= 1.00+0.09−0.08 (stat.) +0.12−0.10 (sys.) pb with an expected (observed) significance of 4.6 (5.5) and 9.5 (9.9) standard deviations from the background-only hypothesis respectively. The measured cross sections are in agreement with the standard model prediction. We use these measurements to constrain the Wilson coefficients for four dimension-six operators which would modify t¯tZ and t¯tW production. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 08 (2018) 011. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The leading order Feynman diagram for tˉtZ, tˉtW production at the LHC. The charge conjugate of the diagrams shown is implied. |
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Figure 1-a:
The leading order Feynman diagram for tˉtW production at the LHC. The charge conjugate of the diagram shown is implied. |
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Figure 1-b:
The leading order Feynman diagram for tˉtZ production at the LHC. The charge conjugate of the diagram shown is implied. |
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Figure 2:
Distribution of different kinematic variables in data compared to the estimated expectations. From left to right: jet multplicity and b-jet multiplicity (top), HT and EmissT (center), trailing lepton pT and event yields (bottom). The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-a:
Distribution of Jet multplicity in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-b:
Distribution of b-jet multiplicity in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-c:
Distribution of HT in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-d:
Distribution of EmissT in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-e:
Distribution of trailing lepton pT in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 2-f:
Distribution of event yields in data compared to the estimated expectation. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 3:
BDT value distribution for background and signal processes. The expected contribution from the different background processes are stacked as well as the expected contribution from the signal. The shaded band represents the uncertainty in the prediction of the background and the signal processes. |
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Figure 4:
Nonprompt control region plots in dilepton channel with BDT < 0: distributions of the total yields versus jet multiplicity and transverse momentum of the trailing lepton. |
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Figure 4-a:
Nonprompt control region plot in dilepton channel with BDT < 0: distribution of the total yields versus jet multiplicity. |
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Figure 4-b:
Nonprompt control region plot in dilepton channel with BDT < 0: distribution of the total yields versus transverse momentum of the trailing lepton. |
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Figure 5:
Nonprompt control region plots in trilepton channel: distributions of the total yields versus lepton channel, missing transverse energy and (b-tagged) jet multiplicity. |
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Figure 5-a:
Nonprompt control region plot in trilepton channel: distribution of the total yields versus lepton channel. |
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Figure 5-b:
Nonprompt control region plot in trilepton channel: distribution of the total yields versus missing transverse energy. |
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Figure 5-c:
Nonprompt control region plot in trilepton channel: distribution of the total yields versus b-tagged jet multiplicity. |
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Figure 5-d:
Nonprompt control region plot in trilepton channel: distribution of the total yields versus jet multiplicity. |
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Figure 6:
WZ control region plots: Distributions of the total yields versus lepton channel, jet multiplicity, transverse mass of the lepton and the missing transverse energy and the reconstructed invariant mass of the Z boson candidates. For all the plots the requirement on jet multiplicity is suppressed. |
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Figure 6-a:
WZ control region plot: Distribution of the total yields versus lepton channel. The requirement on jet multiplicity is suppressed. |
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Figure 6-b:
WZ control region plot: Distribution of the total yields versus jet multiplicity. The requirement on jet multiplicity is suppressed. |
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Figure 6-c:
WZ control region plot: Distribution of the total yields versus the transverse mass of the lepton and the missing transverse energy. The requirement on jet multiplicity is suppressed. |
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Figure 6-d:
WZ control region plot: Distribution of the total yields versus the reconstructed invariant mass of the Z boson candidates. The requirement on jet multiplicity is suppressed. |
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Figure 7:
Data-MC comparison for the Z candidates mass (top left), event yields (top right), jet multiplicity (bottom left) and b-jet multiplicity (bottom right) in a ZZ-dominated background control region |
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Figure 7-a:
Data-MC comparison for the Z candidates mass in a ZZ-dominated background control region |
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Figure 7-b:
Data-MC comparison for the event yields in a ZZ-dominated background control region |
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Figure 7-c:
Data-MC comparison for the jet multiplicity in a ZZ-dominated background control region |
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Figure 7-d:
Data-MC comparison for the b-jet multiplicity in a ZZ-dominated background control region |
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Figure 8:
Distributions of the predicted and observed yields versus the kinematic variables in tˉtW signal enriched region for same charge dilepton channel. |
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Figure 8-a:
Distribution of the predicted and observed yields in tˉtW signal enriched region for same charge dilepton channel. |
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Figure 8-b:
Distribution of the predicted and observed yields in tˉtW signal enriched region for same charge dilepton channel. |
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Figure 8-c:
Distribution of the predicted and observed yields in tˉtW signal enriched region for same charge dilepton channel. |
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Figure 8-d:
Distribution of the predicted and observed yields in tˉtW signal enriched region for same charge dilepton channel. |
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Figure 9:
Distributions of the predicted and observed yields versus the kinematic variables in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-a:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-b:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-c:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-d:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-e:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 9-f:
Distribution of the predicted and observed yields in tˉtZ signal enriched region for three lepton channel. |
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Figure 10:
Post-fit predicted and observed yields in each analysis bin in the same-sign dilepton analysis.The hatched band shows the total uncertainty associated to signal and background predictions. |
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Figure 11:
Post-fit predicted and observed yields in Njets= 2, 3 and ≥4 categories in the three-lepton analyses. The hatched band shows the total uncertainty associated to signal and background predictions. |
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Figure 12:
Post-fit predicted and observed yields in the four-lepton analyses. The hatched band shows the total uncertainty associated to signal and background predictions. |
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Figure 13:
The result of the two-dimensional best fit for tˉtW and tˉtZ 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 tˉtW and tˉtZ cross section measurements, and the corresponding 1σ bands, obtained from the dilepton, and the three-lepton/four-lepton channels, respectively. The figure also shows the predictions from theory and the corresponding uncertainties. |
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Figure 14:
Leading order Feynman diagrams involving NP vertices due to the operator which is proportional to ˉcuB, ˉcuW, and ˉcHu (left), and ˉcu (right). |
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Figure 14-a:
Leading order Feynman diagram involving the NP vertex due to the operator which is proportional to ˉcuB, ˉcuW, and ˉcHu. |
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Figure 14-b:
Leading order Feynman diagram involving the NP vertex due to the operator which is proportional to ˉcu. |
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Figure 15:
Signal strength as a function of cj for ˉcuW (top left), ˉcu (top right), ˉcuB (bottom left), and ˉcHu (bottom right). All three processes are affected by ˉcuW, while only tˉtH is affected by ˉcu and only tˉtZ is affected by ˉcHu. Both tˉtZ and tˉtH are sensitive to ˉcuB. |
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Figure 15-a:
Signal strength as a function of cj for ˉcuW. All three processes are affected by ˉcuW. |
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Figure 15-b:
Signal strength as a function of cj for ˉcu. Only tˉtH is affected by ˉcu. |
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Figure 15-c:
Signal strength as a function of cj for ˉcuB. Both tˉtZ and tˉtH are sensitive to ˉcuB. |
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Figure 15-d:
Signal strength as a function of cj for ˉcHu. Only tˉtZ is affected by ˉcHu. |
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Figure 16:
The 1D test statistic q(cj) scan versus cj, profiling all other nuisance parameters, for ˉcuW (top left), ˉcu (top right), ˉcuB (bottom left), and ˉcHu (bottom right). The best-fit value is indicated by a solid line. Dotted lines and dashed lines indicate 1 σ CLs and 2 σ CLs, respectively. |
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Figure 16-a:
The 1D test statistic q(cj) scan versus cj, profiling all other nuisance parameters, for ˉcuW. The best-fit value is indicated by a solid line. Dotted lines and dashed lines indicate 1 σ CLs and 2 σ CLs, respectively. |
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Figure 16-b:
The 1D test statistic q(cj) scan versus cj, profiling all other nuisance parameters, for ˉcu. The best-fit value is indicated by a solid line. Dotted lines and dashed lines indicate 1 σ CLs and 2 σ CLs, respectively. |
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Figure 16-c:
The 1D test statistic q(cj) scan versus cj, profiling all other nuisance parameters, for ˉcuB. The best-fit value is indicated by a solid line. Dotted lines and dashed lines indicate 1 σ CLs and 2 σ CLs, respectively. |
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Figure 16-d:
The 1D test statistic q(cj) scan versus cj, profiling all other nuisance parameters, for ˉcHu. The best-fit value is indicated by a solid line. Dotted lines and dashed lines indicate 1 σ CLs and 2 σ CLs, respectively. |
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Figure 17:
The tˉtZ and tˉtW cross section corresponding to the best-fit value of ˉcuW (top left), ˉcu (top right), ˉcuB (bottom left), and ˉcHu (bottom right) is shown as a star, along with the corresponding 1σ (red) and 2σ (blue) contours. The two-dimensional best fit to the tˉtW and tˉtZ cross sections is shown as a cross symbol. Predictions from theory at NLO (dotted lines) and their uncertanties (hatches) are also shown. |
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Figure 17-a:
The tˉtZ and tˉtW cross section corresponding to the best-fit value of ˉcuW is shown as a star, along with the corresponding 1σ (red) and 2σ (blue) contours. The two-dimensional best fit to the tˉtW and tˉtZ cross sections is shown as a cross symbol. Predictions from theory at NLO (dotted lines) and their uncertanties (hatches) are also shown. |
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Figure 17-b:
The tˉtZ and tˉtW cross section corresponding to the best-fit value of ˉcu is shown as a star, along with the corresponding 1σ (red) and 2σ (blue) contours. The two-dimensional best fit to the tˉtW and tˉtZ cross sections is shown as a cross symbol. Predictions from theory at NLO (dotted lines) and their uncertanties (hatches) are also shown. |
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Figure 17-c:
The tˉtZ and tˉtW cross section corresponding to the best-fit value of ˉcuB is shown as a star, along with the corresponding 1σ (red) and 2σ (blue) contours. The two-dimensional best fit to the tˉtW and tˉtZ cross sections is shown as a cross symbol. Predictions from theory at NLO (dotted lines) and their uncertanties (hatches) are also shown. |
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Figure 17-d:
The tˉtZ and tˉtW cross section corresponding to the best-fit value of ˉcHu is shown as a star, along with the corresponding 1σ (red) and 2σ (blue) contours. The two-dimensional best fit to the tˉtW and tˉtZ cross sections is shown as a cross symbol. Predictions from theory at NLO (dotted lines) and their uncertanties (hatches) are also shown. |
| Tables | |
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Table 1:
Summary of the sources of uncertainties, their magnitudes and effects. The first column shows the input uncertainty on each background and signal, while the second and third columns are the postfit uncertainties on tˉtW and tˉtZ cross-section measurements respectively. |
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Table 2:
Post-fit predicted and observed yields in same-sign dilepton final state for BDT < 0 region, i.e. nonprompt control region. The uncertainty represents the total post-fit uncertainty. |
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Table 3:
Post-fit predicted and observed yields in same-sign dilepton final state for 0 < BDT < 0.6 region where the sign of both leptons are negative. The uncertainty represents the total post-fit uncertainty. |
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Table 4:
Post-fit predicted and observed yields in same-sign dilepton final state for BDT > 0.6 region where the sign of both leptons are negative. The uncertainty represents the total post-fit uncertainty. |
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Table 5:
Post-fit predicted and observed yields in same-sign dilepton final state for 0 < BDT < 0.6 region where the sign of both leptons are positive. The uncertainty represents the total post-fit uncertainty. |
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Table 6:
Post-fit predicted and observed yields in same-sign dilepton final state for BDT > 0.6 region where the sign of both leptons are positive. The uncertainty represents the total post-fit uncertainty. |
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Table 7:
Post-fit predicted and observed yields in three-lepton final state in Nbjets= 0 category. The uncertainty represents the total post-fit uncertainty. |
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Table 8:
Post-fit predicted and observed yields in three-lepton final state in Nbjets= 1 category. The uncertainty represents the total post-fit uncertainty. |
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Table 9:
Post-fit predicted and observed yields in three-lepton final state in Nbjets≥ 2 category. The uncertainty represents the total post-fit uncertainty. |
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Table 10:
Post-fit predicted and observed yields in four-lepton final state. The uncertainty represents the total post-fit uncertainty. |
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Table 11:
Summary of expected and observed significance for tˉtW in the same-sign 2-lepton channel and for tˉtZ in the 3-lepton, 4-lepton channels and in the two channels combined. |
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Table 12:
Expected 1σ and 2σ CL for this tˉtW and tˉtZ measurement, for selected Wilson coefficients. |
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Table 13:
Observed best-fit values determined from this tˉtW and tˉtZ measurement, along with corresponding 1σ and 2σ CL intervals for selected Wilson coefficients. |
| Summary |
| A measurement of top quark pair production in association with a W or a Z boson using 13 TeV data is presented. The analysis is performed in the same-sign dilepton final state for tˉtW and the three- and four-lepton final states for tˉtZ, and these three are used to extract the cross sections of tˉtW and tˉtZ production. The same-sign dilepton channel achieves a significance of 5.5 standard deviations, the three-lepton analysis 8.7 standard deviations and the four-lepton analysis 4.6 standard deviatations. From the combination of three- and four-lepton channels a significance of 9.9 standard deviations for tˉtZ is obtained. The measured cross sections are σ(tˉtZ)= 1.00+0.09−0.08 (stat.) +0.12−0.10 (sys.) pb and σ(tˉtW)= 0.80+0.12−0.11 (stat.) +0.13−0.12 (sys.) pb, in agreement with the standard model predictions. These results have been used to set constraints on the Wilson coefficients of four operators which would modify t¯tZ and t¯tW production. |
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