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| CMS-PAS-TOP-15-019 | ||
| Combination of cross-section measurements of associated production of a single top quark and a W boson at $\sqrt{s} =$ 8 TeV with the ATLAS and CMS experiments | ||
| CMS Collaboration | ||
| May 2016 | ||
| Abstract: A combination of cross-section measurements for the associated production of a top quark and a W boson in proton-proton collisions at $\sqrt{s}=$ 8 TeV by the ATLAS and CMS experiments is presented. The two measurements are based on integrated luminosities of 20.3 fb$^{-1}$ and 12.2 fb$^{-1}$, respectively. The combined production cross-section of a single top quark and a W boson is determined as 23.1 $\pm$ 1.1 (stat) $\pm$ 3.3 (syst) $\pm$ 0.8 (lumi) pb = 23.1 $\pm$ 3.6 pb, in agreement with the NLO+NNLL expectation. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Cross-section measurements for the associated production of a top quark and a W boson performed by ATLAS and CMS, and combined result compared with the NLO+NNLL prediction [34] (gray bands). The uncertainties in the theoretical prediction are represented by dark and light gray bands for renormalisation/factorisation scale and PDF (evaluated using MSTW2008 [36]), respectively. |
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Figure 2:
Results of the stability tests performed on the correlation assumptions about the uncertainty categories. For each test the correlation factor $\rho $ is varied from its default value to a test value and the corresponding shifts on the measured uncertainty are reported. No effect is observed on the combined central value. |
| Tables | |
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Table 1:
Uncertainty components, their magnitude (relative to the individual measurements) and correlation ($\rho $) between the ATLAS and CMS measurements. Uncertainties in the same row can be compared between experiments as detailed in the text and in Refs. [26,27]. The naming conventions follow those from the corresponding experiments. |
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Table 2:
Contribution of each uncertainty category to the combined cross-section uncertainty. |
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Table 3:
Contribution of each theory modelling uncertainty to the combination. |
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Table 4:
Results of the stability tests performed on the correlation assumptions about the uncertainty categories. For each test the correlation factor $\rho $ is varied from its default value to a test value and the corresponding shifts on the combined central value and on the measured uncertainty are reported. |
| Summary |
| The ATLAS and CMS collaborations have measured the cross-section for the production of a top quark in association with a W boson in proton--proton collision at $\sqrt{s}= $ 8 TeV. The two cross-section measurements are combined using the best linear unbiased estimator (BLUE) method. The combined cross-section is 23.1 $\pm$ 1.1 (stat) $\pm$ 3.3 (syst) $\pm$ 0.8 (lumi) pb, in agreement with the NLO+NNLL prediction. This corresponds to a decrease of the total uncertainty by 0.3 pb compared to the most precise individual measurement. The dominant uncertainties on the combined measurement are due to theory modelling. The form factor times CKM matrix element is determined to be $| f_{\textrm{LV}} V_{\mathrm{tb}} | =$ 1.02 $\pm$ 0.09. |
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