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| CMS-PAS-TOP-16-003 | ||
| Measurement of the inclusive cross section of single top-quark production in the $t$-channel at 13 TeV | ||
| CMS Collaboration | ||
| March 2016 | ||
| Abstract: The $t$ channel single top quark production cross section is measured in proton proton collisions at 13 TeV with the CMS detector at the CERN LHC. The analyzed data correspond to an integrated luminosity of 2.3 fb$^{-1}$. After a selection optimized for the $t$ channel single top quark production with a muon+jets signature in the final state, several kinematic variables are combined into one multivariate discriminator optimized to separate signal from background events. A fit to the distribution of the discriminating variable yields cross sections of $\sigma_{t\textrm{-ch.,t}} =$ 141.5 $\pm$ 6.7 (stat) $\pm$ 9.4 (exp) $^{+19.3}_{-19.6}$ (theo) $\pm$ 3.8 (lumi) pb and $\sigma_{t\textrm{-ch.,}\bar{\textrm{t}}} =$ 81.0 $\pm$ 6.2 (stat) $\pm$ 8.1 (exp) $^{+10.9}_{-10.9}$ (theo) $\pm$ 2.2 (lumi) pb for the production of single top quarks and single top anti-quarks, respectively. From the measured inclusive cross section, $\sigma_{t\textrm{-ch.}} =$ 227.8 $\pm$ 9.1 (stat) $\pm$ 14.0 (exp) $^{+28.7}_{-27.7}$ (theo) $\pm$ 6.2 (lumi) pb, and the predicted value the CKM matrix element $V_{\mathrm{tb}}$ is calculated to be $|V_{\mathrm{tb}}| =$ 1.02 $\pm$ 0.07 (exp) $\pm$ 0.02 (theo). All results are in agreement with the standard model predictions. | ||
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These preliminary results are superseded in this paper, PLB 772 (2017) 752. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1-a:
Feynman diagrams for single top quark production in the $t$ channel: (a) 2$\rightarrow $2 and (b) 2$\rightarrow $3 processes. |
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Figure 1-b:
Feynman diagrams for single top quark production in the $t$ channel: (a) 2$\rightarrow $2 and (b) 2$\rightarrow $3 processes. |
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Figure 2-a:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (a), for positively charged muons only (b), and for negatively charged muons only (c). The QCD fit template is derived from a sideband region in data. Only statistical uncertainties are taken into account in the fit. |
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Figure 2-b:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (a), for positively charged muons only (b), and for negatively charged muons only (c). The QCD fit template is derived from a sideband region in data. Only statistical uncertainties are taken into account in the fit. |
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Figure 2-c:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (a), for positively charged muons only (b), and for negatively charged muons only (c). The QCD fit template is derived from a sideband region in data. Only statistical uncertainties are taken into account in the fit. |
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Figure 3-a:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-b:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-c:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-d:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-e:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-f:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-g:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-h:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 3-i:
Neural network distributions for all (a,d,g), positively (b,e,h) and negatively charged muons (c,f,i) normalized to the yields obtained from the simultaneous fit in the 2j1t (a,b,c), 3j1t (d,e,f) and 3j2t region (g,h,i). The shaded areas indicate the post-fit uncertainties. |
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Figure 4:
Comparison of the measured $R_{t\textrm {-ch.}}$ with the prediction obtained using different PDF sets: MRST2006 [46], MSTW2008NLO [47], HERAPDF[48], CTEQ6.6 [49], CT10 [50], and NNPDF [51]. In case of MSTW2008NLO and of NNPDF the fixed four-flavour scheme PDFs are used together with the POWHEG 4FS calculation. The POWHEG calculation in the 5FS is used for all other PDFs, as they are are variable flavor scheme PDFs. The nominal value for the top quark mass is 173.0 GeV. Error bars for the different PDF sets include the statistical uncertainty, the uncertainty on the factorisation and renormalization scales, derived varying both of them them by a factor 0.5 and 2, and the uncertainty on the top quark mass, derived varying the top quark mass between 172.0 and 174.0 GeV. |
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Figure 5:
The $t$ channel single top quark cross section summary of the most precise CMS measurements in comparison with NLO+NNLL QCD calculations. The Tevatron measurements are also shown. |
| Tables | |
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Table 1:
Event yields for the main processes in the 2-jets-1-tag sample. Except for the number of QCD multi-jet events all yields are taken from simulation. The quoted uncertainties are statistical uncertainties only and are due to the limited size of the samples of simulated events. The yield of QCD multi-jet events is determined from the data (see Sec. 3). The W+jets process is modelled using the LO MadGraph generator, rescaled to NLO accuracy using the selection efficiency observed in events generated with MG5-aMC@NLO. |
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Table 2:
Input variables used in the neural network ranked according to their importance. |
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Table 3:
Scale factors from the fits for the signal process and the background categories. The uncertainties include the statistical uncertainty and the experimental sources of uncertainty that are considered as nuisance parameters in the fit. |
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Table 4:
Relative impact of systematic uncertainties with respect to the observed cross section value $\sigma _{t{\rm -ch.},\mathrm{ t + \bar{t} }}^{\rm {obs}}$, $\sigma _{t{\rm -ch.},t}^{\rm {obs}}$ and $\sigma _{t{\rm -ch.},\mathrm{ \bar{t} }}^{\rm {obs}}$, given in percent. Uncertainties are grouped and summed together with the method suggested in [39]. |
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Table 5:
Relative impact of the experimental systematic uncertainties with respect to the observed cross section value $\sigma _{t{\rm -ch.},\mathrm{ t + \bar{t} }}^{\rm {obs}}$, $\sigma _{t{\rm -ch.},t}^{\rm {obs}}$ and $\sigma _{t{\rm -ch.},\mathrm{ \bar{t} }}^{\rm {obs}}$, given in percent. These estimates are obtained by fixing one uncertainty at a time and considering all others as nuisance parameters in the fit and comparing to the uncertainty obtained when treating all uncertainty sources as nuisance parameters. These numbers are for illustration purpose only, the uncertainty quoted for the result is the total experimental uncertainty from the fit. |
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