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| CMS-TOP-16-003 ; CERN-EP-2016-233 | ||
| Cross section measurement of $t$-channel single top quark production in pp collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 3 October 2016 | ||
| Phys. Lett. B 772 (2017) 752 | ||
| Abstract: The cross section for the production of single top quarks in the $t$ channel is measured in proton-proton collisions at 13 TeV with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 2.2 fb$^{-1}$. The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 238 $\pm$ 13 (stat) $\pm$ 29 (syst) pb and a ratio of top quark and top antiquark production of $R_{t\text{-ch.}}= $ 1.81 $\pm$ 0.18 (stat) $\pm$ 0.15 (syst). From the total cross section the absolute value of the CKM matrix element $V_{\mathrm{ t }\mathrm{ b }}$ is calculated to be 1.05 $\pm$ 0.07 (exp) $\pm$ 0.02 (theory). All results are in agreement with the standard model predictions. | ||
| Links: e-print arXiv:1610.00678 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
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-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:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (left), for positively charged muons only (middle), and for negatively charged muons only (right). 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-a:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample. 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, for positively charged muons only. 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 for negatively charged muons only. 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-d:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (left), for positively charged muons only (middle), and for negatively charged muons only (right). 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-e:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (left), for positively charged muons only (middle), and for negatively charged muons only (right). 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-f:
Fit to the $ {m_{\mathrm {\rm T}}^{\rm W}} $ distributions in the 2-jets-1-tag sample (left), for positively charged muons only (middle), and for negatively charged muons only (right). 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:
Neural network distributions for all (left), positively (middle), and negatively (right) charged muons normalized to the yields obtained from the simultaneous fit in the 2-jets-1-tag (upper), 3-jets-1-tag (middle), and 3-jets-2-tags region (lower). The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-a:
Neural network distributions for all muons normalized to the yields obtained from the simultaneous fit in the 2-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-b:
Neural network distributions for positively charged muons normalized to the yields obtained from the simultaneous fit in the 2-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-c:
Neural network distributions for negatively charged muons normalized to the yields obtained from the simultaneous fit in the 2-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-d:
Neural network distributions for all muons normalized to the yields obtained from the simultaneous fit in the 3-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-e:
Neural network distributions for positively charged muons normalized to the yields obtained from the simultaneous fit in the 3-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-f:
Neural network distributions for negatively charged muons normalized to the yields obtained from the simultaneous fit in the 3-jets-1-tag region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-g:
Neural network distributions for all muons normalized to the yields obtained from the simultaneous fit in the 3-jets-2-tags region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-h:
Neural network distributions for positively charged muons normalized to the yields obtained from the simultaneous fit in the 3-jets-2-tags region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 3-i:
Neural network distributions for negatively charged muons normalized to the yields obtained from the simultaneous fit in the 3-jets-2-tags region. The ratio between data and simulated distributions after the fit is shown at the bottom of each figure. The hatched areas indicate the post-fit uncertainties. |
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Figure 4:
Comparison of the measured $R_{t\textrm {-ch.}}$ (dotted line) with the prediction from different PDF sets: CT14 NLO [51], ABM11 NLO and ABM12 NNLO [52], MMHT14 NLO [53], HERAPDF2.0 NLO [54], NNPDF 3.0 NLO [55]. The PowHeg 4FS calculation is used. The nominal value for the top quark mass is $172.5 GeV $. The error bars for the different PDF sets include the statistical uncertainty, the uncertainty due to the factorization and renormalization scales, derived varying both of them by a factor 0.5 and 2, and the uncertainty in the top quark mass, derived varying the top quark mass between 171.5 and 173.5 GeV. For the measurement, the inner and outer error bars correspond to the statistical and total uncertainties, respectively. |
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Figure 5:
The summary of the most precise CMS measurements [3,5] for the total $t$-channel single top quark cross section, in comparison with NLO+NNLL QCD calculations [22]. The combination of the Tevatron measurements [56] is also shown. |
| Tables | |
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Table 1:
Event yields for the main processes in the 2-jets-1-tag sample. The quoted uncertainties are statistical only. All yields are taken from simulation, except for QCD multijet events where the yield and the associated uncertainty are determined from data (as discussed in Section 4). |
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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 fit for the normalization of events with a positively charged muon for the signal process, the background categories, and the ratio of single top quark to top antiquark production. The uncertainties include the statistical uncertainty and the experimental sources of uncertainty which 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 sections as well as the top quark to top antiquark cross section ratio. Uncertainties are grouped and summed together with the method suggested in Ref. [45]. |
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Table 5:
Relative impact of the experimental systematic uncertainties included in the fit with respect to the observed cross sections as well as the top quark to top antiquark cross section ratio. The impact due to the size of the samples of simulated events is estimated by comparing the central values obtained by applying or not applying the Barlow-Beeston method in the fit. All other 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 only, the uncertainty quoted for the result is the total experimental uncertainty from the fit. |
| Summary |
| A measurement of the cross section of the $t$-channel single top quark production is presented using events with one muon and jets in the final state. The cross section for the production of single top quarks and the ratio of the top quark to top antiquark production are measured together in a simultaneous fit where the results are used to evaluate the production cross section of single top antiquarks. The measured total cross section, which currently constitutes the most precise result at 13 TeV, is used to calculate the absolute value of the CKM matrix element $ | \mathrm{V_{tb}} | $. All results are in agreement with recent theoretical standard model predictions. |
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Compact Muon Solenoid LHC, CERN |
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