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| CMS-PAS-TOP-24-011 | ||
| Measurement of the $ t $-channel single top quark cross section in pp collision data at $ \sqrt{s} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 2025-07-21 | ||
| Abstract: The single top quark $ t $-channel production cross section is measured in proton-proton collisions at $ \sqrt{s}= $ 5.02 TeV using data recorded in 2017, corresponding to an integrated luminosity of 302 pb$^{-1} $. Events with one electron or muon and two or more jets, among which one or more are identified as coming from a b quark, are analyzed. The combined cross section of single top quark (tq) and single top antiquark ($ \bar{\mathrm{t}} $q) production is $ \sigma(\mathrm{tq} + \mathrm{\bar{t}q})= $ 30.2$ ^{+3.7}_{-3.6}$ (stat) $^{+4.4}_{-4.2}$ (syst) $\pm $ 0.6 (lumi) pb, consistent with the standard model prediction of 30.3$ ^{+0.7}_{-0.5} $ pb. The individual cross sections are measured to be $ \sigma(\mathrm{tq})= $ 21.1$ ^{+3.0}_{-2.8} $ (stat) $^{+2.8}_{-2.7} $ (syst) $\pm$ 0.4 (lumi) pb, and $ \sigma(\mathrm{\bar{t}q})= $ 8.2$ ^{+2.4}_{-2.3} $ (stat) $ ^{+1.9}_{-1.8} $ (syst) $\pm$ 0.2 (lumi) pb. Their ratio, $ \mathcal{R}_{t\text{-ch}} $ is also measured, resulting in $ \mathcal{R}_{t\text{-ch}}= $ 2.6$ ^{+1.1}_{-0.7} $ (stat) $^{+0.7}_{-0.2}$ (syst). The measurements are in good agreement with the standard model predictions at next-to-next-to-leading-order accuracy in quantum chromodynamics. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading-order diagrams for single top quark (left) and single top antiquark (right) production via the $ t \ \mathrm{channel} $. |
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Figure 1-a:
Leading-order diagrams for single top quark (left) and single top antiquark (right) production via the $ t \ \mathrm{channel} $. |
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Figure 1-b:
Leading-order diagrams for single top quark (left) and single top antiquark (right) production via the $ t \ \mathrm{channel} $. |
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Figure 2:
Observed and predicted number of events in each of the twelve categories of the signal region, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. All uncertainties considered in the analysis are included in the uncertainty band. The lower panels show the data-to-prediction ratio. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 3:
Observed and predicted distributions of the leading jet $ \eta $ (left) and $ p_{\mathrm{T}} $ (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 3-a:
Observed and predicted distributions of the leading jet $ \eta $ (left) and $ p_{\mathrm{T}} $ (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 3-b:
Observed and predicted distributions of the leading jet $ \eta $ (left) and $ p_{\mathrm{T}} $ (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 4:
Observed and predicted distributions of the most discriminating input variable used in the random forest training, $ |\eta_{\mathrm{u_{0}}}| $ (left), and the output MVA discriminator (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 4-a:
Observed and predicted distributions of the most discriminating input variable used in the random forest training, $ |\eta_{\mathrm{u_{0}}}| $ (left), and the output MVA discriminator (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 4-b:
Observed and predicted distributions of the most discriminating input variable used in the random forest training, $ |\eta_{\mathrm{u_{0}}}| $ (left), and the output MVA discriminator (right), in the 2j1b category, before the maximum likelihood fit. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty in the prediction. The lower panels show the data-to-prediction ratio. The first and last bins in each distribution include underflow and overflow events, respectively. The normalizations of the processes are those of the SM predictions except for QCD, which is estimated from data. |
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Figure 5:
Distributions for the $ \ell^{+} $+jets (upper plot) and $ \ell^{-} $+jets (lower plot) categories where the prediction parameters are set to the values obtained in the fit. They show the MVA score and $ |\eta_{u_{0}}| $ distributions, which are the fitted variables in the ML fit in the 2j1b category and the categories with three jets, respectively. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty of the prediction. All uncertainties considered in the analysis are included in the uncertainty band. The lower panels show the ratio of data to prediction. The first and last bins in each distribution include underflow and overflow events, respectively. |
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Figure 5-a:
Distributions for the $ \ell^{+} $+jets (upper plot) and $ \ell^{-} $+jets (lower plot) categories where the prediction parameters are set to the values obtained in the fit. They show the MVA score and $ |\eta_{u_{0}}| $ distributions, which are the fitted variables in the ML fit in the 2j1b category and the categories with three jets, respectively. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty of the prediction. All uncertainties considered in the analysis are included in the uncertainty band. The lower panels show the ratio of data to prediction. The first and last bins in each distribution include underflow and overflow events, respectively. |
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Figure 5-b:
Distributions for the $ \ell^{+} $+jets (upper plot) and $ \ell^{-} $+jets (lower plot) categories where the prediction parameters are set to the values obtained in the fit. They show the MVA score and $ |\eta_{u_{0}}| $ distributions, which are the fitted variables in the ML fit in the 2j1b category and the categories with three jets, respectively. The vertical error bars represent the statistical uncertainty associated to the data, and the hatched band the uncertainty of the prediction. All uncertainties considered in the analysis are included in the uncertainty band. The lower panels show the ratio of data to prediction. The first and last bins in each distribution include underflow and overflow events, respectively. |
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Figure 6:
Two-dimensional 68 and 95% confidence level regions for the signal strengths modifying the top quark and top antiquark cross sections individually, represented by the solid and dashed lines respectively. The blue cross indicates the SM prediction and the the red dot, the best fit for both signal strengths. |
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Figure 7:
Summary of the CMS measurements of the $ t $-channel single top quark production cross section as a function of $ \sqrt{s} $. |
| Tables | |
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Table 1:
Summary of simulated samples used to model the signal and background processes. The last column corresponds to the pQCD and EW order of approximation used to normalize the distributions provided by the generators. The predictions for $ \mathrm{t} \overline{\mathrm{t}} $ and $ t $-channel and $ \mathrm{t}\mathrm{W} $ single top quark production are calculated with the PDF4LHC prescription [46]. For the $ \mathrm{t}\mathrm{W} $ process, approximate NNLO refers to NLO calculations with the addition of soft gluon resummation at NNLL, where a logarithmic expansion of soft and collinear gluon radiation is used. |
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Table 2:
Summary of the variables used for training the MVA classifier in the 2j1b categories. The variables are ordered according to their discriminating power, assessed via the mean decrease in impurity method [50]. ``Leading'' jet refers to the jet with the highest $ p_{\mathrm{T}} $ in the event. |
| Summary |
| A measurement of the single top quark $ t $-channel production cross section in proton-proton collisions at a centre-of-mass energy of 5.02 TeV is performed for events with one electron or one muon and multiple jets using data collected by the CMS experiment in 2017 in conditions of low number of additional interactions per bunch crossing, corresponding to an integrated luminosity of 302 pb$^{-1}$. The main background in the analysis originate from W+jets and top quark pair production, both estimated using simulation. Smaller contributions from quantum chromodynamics multijet events are derived from data. The cross section is measured using a maximum likelihood fit to twelve event categories defined in terms of the number of jets, b-tagged jets, lepton flavour and electrical charge. The cross sections are found to be $ \sigma(\mathrm{t} \mathrm{q} + \overline{\mathrm{t}} \mathrm{q})= $ 30.2$ ^{+3.7}_{-3.6} $ (stat) $^{+4.4}_{-4.2}$ (syst) $\pm$ 0.6 (lumi) pb, $ \sigma(\mathrm{t} \mathrm{q})= $ 21.1$ ^{+3.0}_{-2.8} $ (stat) $^{+2.8}_{-2.7}$ (syst) $\pm$ 0.4 (lumi) pb and $ \sigma(\overline{\mathrm{t}} \mathrm{q})= $ 8.2$ ^{+2.4}_{-2.3} $ (stat) $^{+1.9}_{-1.8}$ (syst) $\pm$ 0.2 (lumi) pb. The ratio between the individual cross sections is found to be $ \mathcal{R}_{t\text{-ch}}= $ 2.6$ ^{+1.1}_{-0.7} $ (stat) $^{+0.7}_{-0.2}$ (syst). All the results are in good agreement with the standard model predictions. |
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