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%\section{Systematics Uncertainties on the Background Prediction} |
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%\label{sec:systematics} |
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[ADD INTRODUCTORY BLURB ON UNCERTAINTIES \\ |
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ADD COMPARISONS OF ALL THE ALTERNATIVE SAMPLES FOR ALL THE SIGNAL |
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REGIONS \\ |
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LIST ALL THE UNCERTAINTIES INCLUDED AND THEIR VALUES] |
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\subsection{Uncertainty on the \ttll\ Acceptance} |
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The \ttbar\ background prediction is obtained from MC, with corrections |
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Pythia (LO). It may also be noted that MC@NLO uses Herwig6 for the |
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hadronisation, while POWHEG uses Pythia6. |
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\item Modeling of taus: The alternative sample does not include |
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Tauola and is otherwise identical to the Powheg sample. |
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Tauola and is otherwise identical to the Powheg sample. |
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This effect was studied earlier using 7~TeV samples and found to be negligible. |
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\item The PDF uncertainty is estimated following the PDF4LHC |
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recommendations[CITE]. The events are reweighted using alternative |
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PDF sets for CT10 and MSTW2008 and the uncertainties for each are derived using the |
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addition, the NNPDF2.1 set with 100 replicas. The central value is |
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determined from the mean and the uncertainty is derived from the |
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$1\sigma$ range. The overall uncertainty is derived from the envelope of the |
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alternative predictions and their uncertainties. |
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\end{itemize} |
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alternative predictions and their uncertainties. |
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This effect was studied earlier using 7~TeV samples and found to be negligible. |
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\end{itemize} |
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\begin{figure}[hbt] |
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%\end{table} |
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\subsubsection{Isolated Track Veto: Tag and Probe Studies} |
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\subsection{Isolated Track Veto: Tag and Probe Studies} |
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[EVERYTHING IS 7TEV HERE, UPDATE WITH NEW RESULTS \\ |
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ADD TABLE WITH FRACTION OF EVENTS THAT HAVE A TRUE ISOLATED TRACK] |
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In this section we compare the performance of the isolated track veto in data and MC using tag-and-probe studies |
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with samples of Z$\to$ee and Z$\to\mu\mu$. The purpose of these studies is to demonstrate that the efficiency |
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{\bf fix me: What you have written in the next paragraph does not explain how $\epsilon_{fake}$ is measured. |
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Why not measure $\epsilon_{fake}$ in the b-veto region?} |
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A measurement of the $\epsilon_{fake}$ in data is non-trivial. However, it is |
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possible to correct for differences in the $\epsilon_{fake}$ between data and MC by |
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applying an additional scale factor for the single lepton background |
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alone, using the sample in the \mt\ peak region. This scale factor is determined after applying the isolated track |
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veto and after subtracting the \ttll\ component, corrected for the |
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isolation efficiency derived previously. |
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As shown in Figure~\ref{fig:vetoeffcomp}, the efficiency for selecting an |
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isolated track in single lepton events is independent of \mt\, so the use of |
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an overall scale factor is justified to estimate the contribution in |
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the \mt\ tail. |
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|
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\begin{figure}[hbt] |
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\begin{center} |
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\includegraphics[width=0.5\linewidth]{plots/vetoeff_comp.png} |
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\caption{ |
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\label{fig:vetoeffcomp}%\protect |
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Efficiency for selecting an isolated track comparing |
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single lepton \ttlj\ and dilepton \ttll\ events in MC and |
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data as a function of \mt. The |
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efficiencies in \ttlj\ and \ttll\ exhibit no dependence on |
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\mt\, while the data ranges between the two. This behavior |
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is expected since the low \mt\ region is predominantly \ttlj, while the |
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high \mt\ region contains mostly \ttll\ events.} |
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\end{center} |
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\end{figure} |
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%A measurement of the $\epsilon_{fake}$ in data is non-trivial. However, it is |
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%possible to correct for differences in the $\epsilon_{fake}$ between data and MC by |
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%applying an additional scale factor for the single lepton background |
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%alone, using the sample in the \mt\ peak region. This scale factor is determined after applying the isolated track |
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%veto and after subtracting the \ttll\ component, corrected for the |
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%isolation efficiency derived previously. |
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%As shown in Figure~\ref{fig:vetoeffcomp}, the efficiency for selecting an |
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%isolated track in single lepton events is independent of \mt\, so the use of |
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%an overall scale factor is justified to estimate the contribution in |
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%the \mt\ tail. |
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% |
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%\begin{figure}[hbt] |
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% \begin{center} |
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% \includegraphics[width=0.5\linewidth]{plots/vetoeff_comp.png} |
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% \caption{ |
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% \label{fig:vetoeffcomp}%\protect |
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% Efficiency for selecting an isolated track comparing |
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% single lepton \ttlj\ and dilepton \ttll\ events in MC and |
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% data as a function of \mt. The |
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% efficiencies in \ttlj\ and \ttll\ exhibit no dependence on |
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% \mt\, while the data ranges between the two. This behavior |
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% is expected since the low \mt\ region is predominantly \ttlj, while the |
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% high \mt\ region contains mostly \ttll\ events.} |
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% \end{center} |
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%\end{figure} |
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