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\newpage \section{\label{sub:Results-of-the}\boldmath$b$ and \boldmath$\tau$ selections} In the next step we applied the requirements of tight $\tau$- and $b$-tagging. Table \ref{cap:btaggingandtau} shows the selection criteria that we applied to data and MC. The b-tag operating point used was TIGHT, which corresponds to NNbtag $>$ 0.775. We chose the $\tau$ with the highest $NN_{\tau}$ as \textit{the} $\tau$ candidate. At this stage of the analysis we separated the events dataset we deal with into parts, according to which type of $\tau$ the candidate with highest NN belongs. This was done primarily to separate the type 3 tau events (which are expected to have much higher fake rate and thus weaker $\ttbar$ cross section result) from the type 2 events. The separate measurement channels were later combined to get the final result (Section \ref{sub:xsect}). In principle, types 1 and 2 should be separated as well but as there exists a considerable cross-migration between them \cite{tau-id} and type 1 is a small fraction of the total (10\% of type 1, 54.5\% of type 2 and 35.5\% of type 3), they were taken togetther in this analysis. The topological NN used to enhance the signal content is described in section \ref{sub:NN-variables} . %Table \ref{b and tau type 3} shows the same efficiencies for %type 3. We see that for type 3 $\tau$ candidates (which are more jet-like then other types) twice more %candidate events are selected due to high $\tau$ fake rate. At this point, we used these ID algorithms to define 3 mutually exclusive and exhastive subsamples out of the original preselected data sample: \begin{itemize} \item The {}``non-$b$ veto'' or {}``signal'' sample - the $\tau$ candidate has $NN_{\tau}>0.90$ ($NN_{\tau}$ denotes the NN cut commonly applied to all taus) for taus types 1 and 2 and $NN(\tau)>0.95$ for taus type 3, and at least one NN b-tag (as in Table \ref{cap:btaggingandtau}). These $NN(\tau)$ cuts were chosen based on previous studies involving hadronic decays of taus \cite{tes,higgs_tau}. This is the sample used to extract the cross section. Jets matched to $\tau$ candidates are not $b$-tagged, althought they still count as jets. \item The {}``$\tau$ veto sample'' or ``loose-tight $\tau$ sample'' - Same selection, but with $0.3<NN_{\tau}<0.7$ for all taus. $\tau$ NN lower cut of 0.3 instead of 0.0 was chosen to bias their jet properties closer to those of tight tau candidates, in particular, so they have narrow showers. The upper cut is at 0.7 and not 0.95 or 0.90 to reduce signal contamination. In this sample, 1400000 events were used for NN training for taus type 1 and 2 and 600000 events were used in the case of type 3 taus. In both cases, the rest of the samples served as QCD template. \item The {}``$b$ veto'' sample - Require exactly 0 tight $b$-tags. This is the control sample used to verify the validity of the QCD modelling method. The b veto requirement implies this sample is almost purely background. \end{itemize} % Along with the $NN_{\tau}$ cut described above, we also applied the cut NNelec $>$ 0.9 only to type 2 taus since these are more likely to be faked by electrons. The cut NNelec $>$ 0.9 was chosen in order to match the lowest cut of $NN_{\tau}$ $>$ 0.9 applied to type 2 taus (Section \ref{sub:Results-of-the}). As both b and $\tau$ ID is the step immediately after the preselection, the number of events available is 2800000 million events. As explained above 1400000 events were used for taus type 1 and 2 NN training and 600000 for type 3 taus NN training. Thus, there are 1400000 events available in each sample for the measurement in the case of types 1 and 2 and 2200000 in the case of type 3. Details on NN training are given in Section \ref{sub:NN-variables}. The QCD modelling method used here is the same as used in p17 and is described in Section IXA of \cite{p17_note}. The final number of events in each channel for both signal and $b$ veto samples is shown on Tables \ref{b_and_tau_type1_2}, \ref{b_and_tau_type_3}, \ref{bveto_type1_2} and \ref{b_veto_type_3} (only statistical uncertainties are shown). As important as determining the subsamples to be used in this analysis, a determination as precise as possible of both signal and electroweak contamination in the ``loose-tight $\tau$ sample'' had be done in order to know whether this sample is totally QCD dominated or not. Numbers showing the composition of such sample are shown on Tables \ref{loosetight1_2} and \ref{loosetight_3} with their respective statistical uncertainties. From the $t\bar{t}$ content in each case we are able estimate the signal contamination in the loose-tight sample. Such contaminations are 5.4\% and 3.0\% for taus type 1 and 2 and type 3 respectively when a cross section of 7.46 pb is assumed (Section \ref{sub:mcsample}). Likewise we see that electroweak contaminations are 2.2\% and 0.9\%. As this is the sample used to model the QCD background both signal and electroweak contaminations were taken into account when measuring the cross section in Section \ref{sub:xsect}. \begin{table}[h] \begin{tabular}{ccc} \hline & {\scriptsize data}& {\scriptsize taggingMC}\\ & {\scriptsize $\geq1$ $\tau$ with $|\eta|<2.5$ and $p_{T}>20$ GeV}& {\scriptsize $\geq1$ $\tau$ with $|\eta|<2.5$ and $p_{T}>20$ GeV}\\ & {\scriptsize $\geq1$ NN b-tag}& {\scriptsize $mcweight \cdot TrigWeight \cdot bTagProb \cdot lumiReWeight \cdot PVzReWeight \cdot bFragWeight$ }\\ & {\scriptsize }& %{\scriptsize $\cdot WZPtReweight \cdot tau$\_$nnout$\_$corr$\_$p20 \cdot tau$\_$track$\_$corr$\_$p20$ }\\ {\scriptsize $\cdot WZPtReweight $ }\\ & {\scriptsize $\geq4$ jets with $|\eta|<2.5$ and $p_{T}>20$ GeV}& {\scriptsize $\geq4$ jets with $|\eta|<2.5$ and $p_{T}>20$ GeV}\\ \end{tabular} \caption{$b$-tagging and $\tau$ ID. In the MC, we use the $b$-tagging certified parameterization rather than actual $b$-tagging, that is, we applied the $b$-tagging weight. We also used the triggering weight as computed by the trigger efficiency parameterization as well as luminosity profile and $PV_Z$ reweighting weights. $ mcweight$ is the MC normalization factors (to luminosity), which are different for MC samples with different parton multiplicities in ALPGEN MC samples.}%\end{ruledtabular} \label{cap:btaggingandtau} \end{table} % \begin{table}[h] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# events\\ \hline data& & 386\\ $t\overline{t}\rightarrow\tau+jets$& & 48.03 $\pm$ 0.53&\\ $t\overline{t}\rightarrow e+jets$& & 25.57 $\pm$ 0.36&\\ $t\overline{t}\rightarrow\mu+jets$& & 3.21 $\pm$ 0.14&\\ $t\overline{t}\rightarrow l+l$& & 4.01 $\pm$ 0.07&\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 7.48 $\pm$ 0.30\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 4.68 $\pm$ 0.17\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 5.66 $\pm$ 0.11 \\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 0.93 $\pm$ 0.08\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 0.51 $\pm$ 0.04\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 1.07 $\pm$ 0.10 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.03 $\pm$ 0.01\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.00 $\pm$ 0.00\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.02 $\pm$ 0.01 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.07 $\pm$ 0.02\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.02 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.01 $\pm$ 0.01 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 0.08 $\pm$ 0.03\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 0.00 $\pm$ 0.00\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 0.04 $\pm$ 0.01\\ \hline \end{tabular} \caption{Final number of events in each channel for taus types 1 and 2 $\tau$ after b-tagging, $\tau$ ID and trigger in the signal sample when the assumed cross section is 7.46 pb. An estimate of QCD background is not included.} %\end{ruledtabular} \label{b_and_tau_type1_2} \end{table} % %\clearpage \begin{table}[t] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# of events\\ \hline data& & 459\\ $t\overline{t}\rightarrow\tau+jets$& & 25.88 $\pm$ 0.39&\\ $t\overline{t}\rightarrow e+jets$& & 4.35 $\pm$ 0.16&\\ $t\overline{t}\rightarrow\mu+jets$& & 3.43 $\pm$ 0.14&\\ $t\overline{t}\rightarrow l+l$& & 2.80 $\pm$ 0.06&\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 3.92 $\pm$ 0.17\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 3.26 $\pm$ 0.15\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 4.08 $\pm$ 0.11\\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 0.74 $\pm$ 0.07\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 0.41 $\pm$ 0.03\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 0.80 $\pm$ 0.10 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.00 $\pm$ 0.00\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.01 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.01 $\pm$ 0.01 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.04 $\pm$ 0.02\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.01 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.00 $\pm$ 0.00 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 0.12 $\pm$ 0.04\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 0.19 $\pm$ 0.04\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 0.06 $\pm$ 0.01 \\ \hline \end{tabular} \caption{Final number of events in each channel for taus type 3 $\tau$ After b-tagging, $\tau$ ID and trigger in the signal sample when the assumed cross section is 7.46 pb. An estimate of QCD background is not included.}%\end{ruledtabular} \label{b_and_tau_type_3} \end{table} \newpage \begin{table}[t] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# of events\\ \hline data& & 2494 \\ $t\overline{t}\rightarrow\tau+jets$& & 33.57 $\pm$ 0.34\\ $t\overline{t}\rightarrow e+jets$& & 15.67 $\pm$ 0.23&\\ $t\overline{t}\rightarrow\mu+jets$& & 2.30 $\pm$ 0.09&\\ $t\overline{t}\rightarrow l+l$& & 2.69 $\pm$ 0.04&\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 9.29 $\pm$ 0.27\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 31.63 $\pm$ 0.90\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 169.95 $\pm$ 2.68\\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 1.30 $\pm$ 0.11\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 3.15 $\pm$ 0.20\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 16.86 $\pm$ 1.14 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.02 $\pm$ 0.01\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.00 $\pm$ 0.00\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.74 $\pm$ 0.33 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.08 $\pm$ 0.02\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.07 $\pm$ 0.03\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.38 $\pm$ 0.22 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 0.10 $\pm$ 0.03\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 0.00 $\pm$ 0.00\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 1.36 $\pm$ 0.49 \\ \hline \end{tabular} \caption{$b$-veto data set composition for types 1 and 2 $\tau$ when the assumed cross section is 7.46 pb.}%\end{ruledtabular} \label{bveto_type1_2} \end{table} %\clearpage \begin{table}[t] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# of events\\ \hline data& & 3688 \\ $t\overline{t}\rightarrow\tau+jets$& & 19.85 $\pm$ 0.27\\ $t\overline{t}\rightarrow e+jets$& & 3.53 $\pm$ 0.13\\ $t\overline{t}\rightarrow\mu+jets$& & 2.80 $\pm$ 0.10\\ $t\overline{t}\rightarrow l+l$& & 1.81 $\pm$ 0.03\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 5.26 $\pm$ 0.19\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 22.43 $\pm$ 0.80\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 126.41 $\pm$ 2.60 \\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 0.92 $\pm$ 0.09\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 2.86 $\pm$ 0.20\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 14.53 $\pm$ 1.15 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.00 $\pm$ 0.00\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.08 $\pm$ 0.04\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.31 $\pm$ 0.18 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.04 $\pm$ 0.02\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.05 $\pm$ 0.02\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.05 $\pm$ 0.04 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 0.16 $\pm$ 0.05\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 0.83 $\pm$ 0.15\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 2.31 $\pm$ 0.46 \\ \hline \end{tabular} %\end{ruledtabular} \caption{$b$-veto data set composition for type 3 $\tau$ when the assumed cross section is 7.46 pb.} \label{b_veto_type_3} \end{table} \begin{table}[t] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# of events\\ \hline data& & 1217 \\ $t\overline{t}\rightarrow\tau+jets$& & 32.94 $\pm$ 0.48\\ $t\overline{t}\rightarrow e+jets$& & 17.02 $\pm$ 0.34&\\ $t\overline{t}\rightarrow\mu+jets$& & 14.37 $\pm$ 0.32&\\ $t\overline{t}\rightarrow l+l$& & 2.43 $\pm$ 0.06&\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 6.33 $\pm$ 0.23\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 4.63 $\pm$ 0.19\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 11.34 $\pm$ 0.26\\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 0.50 $\pm$ 0.06\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 0.58 $\pm$ 0.06\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 1.10 $\pm$ 0.13 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.01 $\pm$ 0.01\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.01 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.00 $\pm$ 0.00 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.03 $\pm$ 0.01\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.04 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.02 $\pm$ 0.01 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 1.07 $\pm$ 0.17\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 0.57 $\pm$ 0.10\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 0.36 $\pm$ 0.04 \\ \hline \end{tabular} \caption{loose-tight data set composition for types 1 and 2 $\tau$ when the assumed cross section is 7.46 pb.}%\end{ruledtabular} \label{loosetight1_2} \end{table} \begin{table}[t] %\begin{ruledtabular} \begin{tabular}{cccc} \hline Sample & & \# of events\\ \hline data& & 4733\\ $t\overline{t}\rightarrow\tau+jets$& & 51.16 $\pm$ 0.57\\ $t\overline{t}\rightarrow e+jets$& & 40.02 $\pm$ 0.50\\ $t\overline{t}\rightarrow\mu+jets$& & 48.00 $\pm$ 0.56\\ $t\overline{t}\rightarrow l+l$& & 2.16 $\pm$ 0.05\\ $Wbb+jets\rightarrow$ $l\nu+bb+jets$& & 8.95 $\pm$ 0.27\\ $Wcc+jets\rightarrow$ $l\nu+cc+jets$& & 7.80 $\pm$ 0.23\\ $Wjj+jets\rightarrow$ $l\nu+jj+jets$& & 16.32 $\pm$ 0.30 \\ $Zbb+jets\rightarrow$ $\tau\tau+bb+jets$& & 0.52 $\pm$ 0.05\\ $Zcc+jets\rightarrow$ $\tau\tau+cc+jets$& & 0.46 $\pm$ 0.04\\ $Zjj+jets\rightarrow$ $\tau\tau+jj+jets$& & 1.16 $\pm$ 0.12 \\ $Zbb+jets\rightarrow$ $ee+bb+jets$& & 0.00 $\pm$ 0.00\\ $Zcc+jets\rightarrow$ $ee+cc+jets$& & 0.00 $\pm$ 0.00\\ $Zjj+jets\rightarrow$ $ee+jj+jets$& & 0.01 $\pm$ 0.01 \\ $Zbb+jets\rightarrow$ $\mu\mu+bb+jets$& & 0.06 $\pm$ 0.01\\ $Zcc+jets\rightarrow$ $\mu\mu+cc+jets$& & 0.07 $\pm$ 0.01\\ $Zjj+jets\rightarrow$ $\mu\mu+jj+jets$& & 0.11 $\pm$ 0.02 \\ $Zbb+jets\rightarrow$ $\nu\nu+bb+jets$& & 2.49 $\pm$ 0.24\\ $Zcc+jets\rightarrow$ $\nu\nu+cc+jets$& & 1.90 $\pm$ 0.14\\ $Zjj+jets\rightarrow$ $\nu\nu+jj+jets$& & 1.28 $\pm$ 0.08 \\ \hline \end{tabular} %\end{ruledtabular} \caption{loose-tight data set composition for type 3 $\tau$ when the assumed cross section is 7.46 pb.} \label{loosetight_3} \end{table} \clearpage