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Leading-order Feynman diagram of non-SM production of a single top quark via the FCNC process $u(c)+g\rightarrow t$.

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: Illustration of the estimation of the multijet background by fitting the $\met$ and $\mtw$ distributions in the analysis regions. As representative examples, the $\met$ distribution is shown in the $e^+$ barrel channel in~\subref{fig:barrel_ele_plus_QCDFit_SR} and the $\mtw$ distribution is shown in the $\mu^+$ channel in~\subref{fig:muon_plus_QCDFit_SR}. Both distributions are in the SR. The stacked histograms were normalised to the fit result. The uncertainty band represents the uncertainty due to limited sample size and the rate uncertainties of the different processes ($20$\% for $W$+jets production, $30$\% for the multijet background and $6$\% for the top-quark processes). The ratio of observed to predicted (Pred.) numbers of events in each bin is shown in the lower panel. Events beyond the axis range are included in the last bin. : Caption not extracted

Pie chart of the background composition of the SR. The SR comprises the two electron channels (barrel and endcap) and the muon channel. The pre-fit event yields are reported in Table~\ref{tab:res_evnt_yield_final}.

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: Distributions of the $D_1$ and $D_2$ discriminants for signal and background processes. Each distribution is normalised to unit area. The discriminant $D_1$ was used for $cgt$ analysis and the $\ell^-$ channel of the $ugt$ analysis. The discriminant $D_2$ was used in the $\ell^+$ channel of the $ugt$ analysis. The histograms in~\subref{subfig:D1_cgt} show the distributions obtained in the $cgt$ analysis, that is, the discriminant was evaluated for all selected events independent of $\sgn q(\ell)$. The distributions in the $\ell^+$ channel of the $ugt$ analysis are shown in~\subref{subfig:D2_ugt_plus}. : Caption not extracted

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: : Distributions of the NN discriminants $D_1$ and $D_2$ observed in~\subref{subfig:D_1_tqVR} the \tchanvr, \subref{subfig:D_1_tTbarVR} the \ttvr and \subref{subfig:D_2_WjetsVR} the $\ell^+\;$\wvr. The observed data are compared with the distribution of simulated background events normalised to the number of expected events, accounting for the normalisation factors obtained in the fits of the $\met$ and $\mtw$ distributions for estimating the multijet background. The uncertainty band represents the uncertainty due to limited sample size and the rate uncertainties of the different processes ($20$\% for $W$+jets production, $30$\% for the multijet background and $6$\% for the top-quark processes). The ratio of observed to predicted (Pred.) numbers of events in each bin is shown in the lower panel.

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: The NN discriminants $D_1$ and $D_2$ of the $ugt$ search are shown with the post-fit normalisation applied to the stacked histograms of the different hard-scattering processes. The histograms in \protect\subref{fig:NNout_postfit_D1_ugt_minus_full_dist} and \protect\subref{fig:NNout_postfit_D2_ugt_plus_full_dist} show the full discriminant range in the negatively charged lepton channel and the positively charged lepton channel, respectively. The histograms \protect\subref{fig:NNout_postfit_D1_ugt_minus_zoom_high} and \protect\subref{fig:NNout_postfit_D2_ugt_plus_zoom_high} show a zoomed-in view of the high discriminant region between 0.7 and 1.0. The hatched bands represent the post-fit uncertainty of the total event yield in each bin. Correlations among uncertainties were taken into account as determined in the fit. The fitted signal contribution is included but is barely visible because its relative size is very small. : Caption not extracted

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: The NN discriminant $D_1$ of the $cgt$ search is shown with the post-fit normalisation applied to the stacked histograms of the different hard-scattering processes. The histogram in \protect\subref{fig:NNout_postfit_cgt_full_dist} shows the full discriminant range. The histogram \protect\subref{fig:NNout:postfit_cgt_zoom_high} shows a zoomed-in view of the high discriminant region between $0.7$ and $1.0$. The hatched bands represent the post-fit uncertainty of the total event yield in each bin. Correlations among uncertainties were taken into account as determined in the fit. : Caption not extracted