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This analysis uses several different control regions in addition to the signal regions. |
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All of these different regions are defined in this section. |
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Figure~\ref{fig:venndiagram} illustrates the relationship between these regions. |
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%Figure~\ref{fig:venndiagram} illustrates the relationship between these regions. |
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|
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\subsection{Single Lepton Selections} |
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\subsection{Single Lepton Selection} |
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|
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[UPDATE SELECTION] |
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|
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The single lepton preselection sample is based on the following criteria |
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\begin{itemize} |
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Table.~\ref{tab:DatasetsData}). Dilepton triggers are used only for the dilepton control region. |
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\item select events with one high \pt\ electron or muon, requiring |
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\begin{itemize} |
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\item $\pt>30~\GeVc$ and $|\eta|<2.5(2.1)$ for \E(\M) |
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\item $\pt>30~\GeVc$ and $|\eta|<2.1$ |
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\item satisfy the identification and isolation requirements detailed |
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in the same-sign SUSY analysis (SUS-11-010) for electrons and the opposite-sign |
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SUSY analysis (SUS-11-011) for muons |
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\end{itemize} |
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\item require at least 4 PF jets in the event with $\pt>30~\GeV$ |
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within $|\eta|<2.5$ |
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within $|\eta|<2.5$ out of which at least 1 satisfies the CSV |
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medium working point b-tagging requirement |
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\item require moderate $\met>50~\GeV$ |
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\end{itemize} |
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|
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In addition, we count the number of SSV medium working point b-tags, $N_{b-tag}$. |
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Table~\ref{tab:preselectionyield} shows the yields in data and MC without any corrections for this preselection region. |
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|
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Currently, we focus on the muon channel because it is cleaner (the QCD contribution is negligible) |
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and the triggers are simpler (we use single muon triggers, as opposed to electron + 3-jet triggers). |
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We will add the electron channel, time permitting. However, since this is a systematics-dominated |
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analysis, increasing the statistics by adding the electrons is not expected to significantly improve |
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the sensitivity, especially because the electron selection efficiency is smaller and the systematic |
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uncertainty associated with the QCD background is larger. |
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|
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We then define the following subsamples within this preselection sample: |
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\begin{itemize} |
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\item $N_{b-tag} = 0$, i.e. b-veto region |
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\item $N_{b-tag} \ge 1 $, i.e. b-tagged region |
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\begin{itemize} |
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\item without an additional isolated track veto |
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\item with an additional isolated track veto |
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\end{itemize} |
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\end{itemize} |
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\begin{table}[!h] |
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\begin{center} |
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\begin{tabular}{c|c} |
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\hline |
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\hline |
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\end{tabular} |
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\caption{ Raw Data and MC predictions without any corrections are shown after preselection. \label{tab:preselectionyield}} |
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\end{center} |
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\end{table} |
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|
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For the signal regions, we then furthermore require $\met>100~\GeV$ while some of the background predictions and scale factors |
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are done for both \met |
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requirements to show stability of the method. |
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Within each of these subsamples we then define an \mt peak ($60 < \mt < 100~\GeV$) region and an \mt tail ($\mt > 150~\GeV$) region |
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% |
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We generally use the \mt peak region yields in data and multiply it by the ratio of tail divided by peak in MC times appropriate corrections |
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in order to estimate the background in data in the tail region. |
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\subsection{Signal Region Selection} |
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|
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{\bf We have not looked at the data in the signal region after the first 1 fb$^{-1}$ of data.} |
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The signal regions (SRs) are selected to improve the sensitivity for the |
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single lepton requirements and cover a range of scalar top |
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scenarios. The \mt\ and \met\ variables are used to define the signal |
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regions and the requirements are listed in Table~\ref{tab:srdef}. |
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|
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\subsection{Dilepton control region} |
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\begin{table}[!h] |
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\begin{center} |
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\begin{tabular}{l|c|c} |
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\hline |
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Signal Region & Minimum \mt\ [GeV] & Minimum \met\ [GeV] \\ |
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\hline |
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\hline |
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SRA & 150 & 100 \\ |
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SRB & 120 & 150 \\ |
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SRC & 120 & 200 \\ |
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SRD & 120 & 250 \\ |
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SRE & 120 & 300 \\ |
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\hline |
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\end{tabular} |
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\caption{ Signal region definitions based on \mt\ and \met\ |
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requirements. These requirements are applied in addition to the |
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baseline single lepton selection. |
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\label{tab:srdef}} |
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\end{center} |
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\end{table} |
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|
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We define a dilepton control region requiring two isolated leptons, $ee, e\mu$, or $\mu\mu$ to study the jet multiplicity in data and MC, and derive |
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scale factors based on their consistency. This study is documented in Section~\ref{sec:jetmultiplicity}. |
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Table~\ref{tab:srrawmcyields} shows the expected number of SM |
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background yields for the SRs. A few stop signal yields for four |
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values of the parameters are also shown for comparison. The signal |
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regions with looser requirements are sensitive to lower stop masses |
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M(\sctop), while those with tighter requirements are more sensitive to |
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higher M(\sctop). |
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|
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\begin{table}[!h] |
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\begin{center} |
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\begin{tabular}{l||c|c|c|c} |
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\hline |
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Sample & SRA & SRB & SRC & SRD \\ |
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\hline |
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\hline |
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\ttdl\ & $700 \pm 15$& $408 \pm 12$& $134 \pm 7$& $43 \pm 4$ \\ |
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\ttsl\ \& single top (1\Lep) & $111 \pm 6$& $71 \pm 5$& $15 \pm 2$& $4 \pm 1$ \\ |
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\wjets\ & $58 \pm 35$& $57 \pm 35$& $29 \pm 26$& $26 \pm 26$ \\ |
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Rare & $63 \pm 3$& $40 \pm 3$& $17 \pm 2$& $7 \pm 1$ \\ |
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\hline |
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Total & $932 \pm 39$& $576 \pm 38$& $195 \pm 27$& $80 \pm 26$ \\ |
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\hline |
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\end{tabular} |
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\caption{ Expected SM background contributions, including both muon |
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and electron channels. The uncertainties are statistical only. ADD |
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SIGNAL POINTS. |
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\label{tab:srrawmcyields}} |
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\end{center} |
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\end{table} |
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|
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{\bf Fix me: Need to describe here the actual selection. What lepton pT's, \met , etc. } |
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[1 PARAGRAPH BLURB ABOUT BACKGROUNDS AND INTRODUCE CONTROL REGIONS] |
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|
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This sample is only partially overlapping with the single lepton preselection as it requires the dilepton rather than the single lepton triggers. |
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\subsection{Control Region Selection} |
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|
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\subsection{Corrections to Jets and \met} |
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Control regions (CRs) are used to validate the background estimation |
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procedure and derive systematic uncertainties for some |
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contributions. The CRs are selected to have similar |
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kinematics to the SRs, but have a different requirement in terms of |
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number of b-tags and number of leptons, thus enhancing them in |
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different SM contributions. The four CRs used in this analysis are |
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summarized in Table~\ref{tab:crdef}. |
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|
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\begin{table} |
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\begin{center} |
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{\small |
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\begin{tabular}{l|c|c|c} |
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\hline |
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Selection & \multirow{2}{*}{exactly 1 lepton} & \multirow{2}{*}{exactly 2 |
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leptons} & \multirow{2}{*}{1 lepton + isolated |
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track}\\ |
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Criteria & & & \\ |
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\hline |
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\hline |
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\multirow{4}{*}{0 b-tags} |
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& CR1) W+Jets dominated: |
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& CR2) apply \Z-mass constraint |
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& CR3) not used \\ |
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& |
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& $\rightarrow$ Z+Jets dominated: Validate |
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& \\ |
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& Validate W+Jets \mt\ tail |
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& \ttsl\ \mt\ tail comparing |
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& \\ |
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& |
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& data vs. MC ``pseudo-\mt '' |
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& \\ |
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\hline |
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\multirow{4}{*}{$\ge$ 1 b-tags} |
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& |
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& CR4) Apply \Z-mass veto |
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& CR5) \ttdl, \ttlt\ and \\ |
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& SIGNAL |
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& $\rightarrow$ \ttdl\ dominated: Validate |
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& \ttlf\ dominated: Validate \\ |
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& REGION |
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& ``physics'' modelling of \ttdl\ |
| 142 |
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& \Tau\ and fake lepton modeling/\\ |
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& |
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& |
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& detector effects in \ttdl\ \\ |
| 146 |
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\hline |
| 147 |
> |
\end{tabular} |
| 148 |
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} |
| 149 |
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\caption{Summary of signal and control regions. |
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\label{tab:crdef}%\protect |
| 151 |
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} |
| 152 |
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\end{center} |
| 153 |
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\end{table} |
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|
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|
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\subsection{MC Corrections} |
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|
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[UPDATE SECTION] |
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|
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\subsubsection{Corrections to Jets and \met} |
| 161 |
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|
| 162 |
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The official recommendations from the Jet/MET group are used for |
| 163 |
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the data and MC samples. In particular, the jet |
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based on the global tags GR\_R\_42\_V23 (DESIGN42\_V17) for |
| 167 |
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data (MC). In addition, these jet energy corrections are propagated to |
| 168 |
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the \met\ calculation, following the official prescription for |
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deriving the Type I corrections. It may be noted that events with |
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anomalous ``rho'' pile-up corrections are excluded from the sample since these |
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correspond to events with unphysically large \met\ and \mt\ tail |
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signal region (see Figure~\ref{fig:mtrhocomp}). An additional correction to remove |
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the $\phi$-modulation observed in the \met\ is included, improving |
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the agreement between the data and the MC, as shown in |
| 77 |
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Figure~\ref{fig:metphicomp}. This correction has an effect on this analysis, |
| 78 |
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since the azimuthal angle enters the \mt\ distribution. |
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deriving the Type I corrections. |
| 170 |
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|
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\clearpage |
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|
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\begin{figure}[!ht] |
| 83 |
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\begin{center} |
| 84 |
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\includegraphics[width=0.5\linewidth]{plots/mt_rho_comp.png} |
| 85 |
< |
\caption{ \label{fig:mtrhocomp}%\protect |
| 86 |
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Comparison of the \mt\ distribution for events with |
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unphysical energy corrections ($\rho <0$ or $ \rho > 40$, where $\rho$ is a |
| 88 |
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measure of the average pileup energy density) and the |
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nominal sample. Events with large pileup corrections |
| 90 |
< |
correspond to noisy events. Since this correction is applied |
| 91 |
< |
to the jets and propagated to the \met, these events have |
| 92 |
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anomalously large \met\ and populate the \mt\ tail. These |
| 93 |
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pathological events are excluded from the analysis sample.} |
| 94 |
< |
\end{center} |
| 95 |
< |
\end{figure} |
| 96 |
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|
| 97 |
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\begin{figure}[!hb] |
| 98 |
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\begin{center} |
| 99 |
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\includegraphics[width=0.5\linewidth]{plots/metphi.pdf}% |
| 100 |
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\includegraphics[width=0.5\linewidth]{plots/metphi_phicorr.pdf} |
| 101 |
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\caption{ \label{fig:metphicomp}%\protect |
| 102 |
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The PF \met\ $\phi$ distribution (left) exhibits a |
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modulation. After applying a dedicated correction, the |
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azimuthal dependence is reduced (right).} |
| 105 |
< |
\end{center} |
| 106 |
< |
\end{figure} |
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Events with anomalous ``rho'' pile-up corrections are excluded from the sample since these |
| 172 |
> |
correspond to events with unphysically large \met\ and \mt\ tail |
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signal region. In addition, the recommended MET filters are applied. |
| 174 |
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|
| 108 |
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\clearpage |
| 175 |
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|
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\subsection{Branching Fraction Correction} |
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\subsubsection{Branching Fraction Correction} |
| 177 |
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|
| 178 |
|
The leptonic branching fraction used in some of the \ttbar\ MC samples |
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|
differs from the value listed in the PDG $(10.80 \pm 0.09)\%$. |
| 203 |
|
\end{center} |
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|
\end{table} |
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|
| 206 |
+ |
|
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\subsubsection{Modeling of Additional Hard Jets in Top Dilepton Events} |
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\label{sec:jetmultiplicity} |
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|
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[SUMMARIZE, UPDATE] |
| 211 |
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|
| 212 |
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Dilepton \ttbar\ events have 2 jets from the top decays, so additional |
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jets from radiation or higher order contributions are required to |
| 214 |
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enter the signal sample. The modeling of addtional jets in \ttbar\ |
| 215 |
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events is checked in a \ttll\ control sample, |
| 216 |
+ |
selected by requiring |
| 217 |
+ |
\begin{itemize} |
| 218 |
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\item exactly 2 selected electrons or muons with \pt $>$ 20 GeV |
| 219 |
+ |
\item \met\ $>$ 100 GeV |
| 220 |
+ |
\item $\geq1$ b-tagged jet |
| 221 |
+ |
\item Z-veto |
| 222 |
+ |
\end{itemize} |
| 223 |
+ |
Figure~\ref{fig:dileptonnjets} shows a comparison of the jet |
| 224 |
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multiplicity distribution in data and MC for this two-lepton control |
| 225 |
+ |
sample. After requiring at least 1 b-tagged jet, most of the |
| 226 |
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events have 2 jets, as expected from the dominant process \ttll. There is also a |
| 227 |
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significant fraction of events with additional jets. |
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The 3-jet sample is mainly comprised of \ttbar\ events with 1 additional |
| 229 |
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emission and similarly the $\ge4$-jet sample contains primarily |
| 230 |
+ |
$\ttbar+\ge2$ jet events. Even though the primary \ttbar\ |
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Madgraph sample used includes up to 3 additional partons at the Matrix |
| 232 |
+ |
Element level, which are intended to describe additional hard jets, |
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+ |
Figure~\ref{fig:dileptonnjets} shows a slight mis-modeling of the |
| 234 |
+ |
additional jets. |
| 235 |
+ |
|
| 236 |
+ |
|
| 237 |
+ |
\begin{figure}[hbt] |
| 238 |
+ |
\begin{center} |
| 239 |
+ |
\includegraphics[width=0.5\linewidth]{plots/njets_all_met100_mueg.pdf} |
| 240 |
+ |
\includegraphics[width=0.5\linewidth]{plots/njets_all_met100_diel.pdf}% |
| 241 |
+ |
\includegraphics[width=0.5\linewidth]{plots/njets_all_met100_dimu.pdf} |
| 242 |
+ |
\caption{ |
| 243 |
+ |
\label{fig:dileptonnjets}%\protect |
| 244 |
+ |
Comparison of the jet multiplicity distribution in data and MC for dilepton events in the \E-\M\ |
| 245 |
+ |
(top), \E-\E\ (bottom left) and \M-\M\ (bottom right) channels.} |
| 246 |
+ |
\end{center} |
| 247 |
+ |
\end{figure} |
| 248 |
+ |
|
| 249 |
+ |
It should be noted that in the case of \ttll\ events |
| 250 |
+ |
with a single reconstructed lepton, the other lepton may be |
| 251 |
+ |
mis-reconstructed as a jet. For example, a hadronic tau may be |
| 252 |
+ |
mis-identified as a jet (since no $\tau$ identification is used). |
| 253 |
+ |
In this case only 1 additional jet from radiation may suffice for |
| 254 |
+ |
a \ttll\ event to enter the signal sample. As a result, both the |
| 255 |
+ |
samples with $\ttbar+1$ jet and $\ttbar+\ge2$ jets are relevant for |
| 256 |
+ |
estimating the top dilepton bkg in the signal region. |
| 257 |
+ |
|
| 258 |
+ |
%In this section we discuss a correction to $ N_{2 lep}^{MC} $ in Equation XXX |
| 259 |
+ |
%due to differences in the modelling of the jet multiplicity in data versus MC. |
| 260 |
+ |
%The same correction also enters $ N_{peak}^{MC}$ in Equation XXX to the extend that the |
| 261 |
+ |
%dilepton contributions to $ N_{peak}^{MC}$ gets corrected. |
| 262 |
+ |
|
| 263 |
+ |
%The dilepton control sample is defined by the following requirements: |
| 264 |
+ |
%\begin{itemize} |
| 265 |
+ |
%\item Exactly 2 selected electrons or muons with \pt $>$ 20 GeV |
| 266 |
+ |
%\item \met\ $>$ 50 GeV |
| 267 |
+ |
%\item $\geq1$ b-tagged jet |
| 268 |
+ |
%\end{itemize} |
| 269 |
+ |
% |
| 270 |
+ |
%This sample is dominated by \ttll. The distribution of \njets\ for data and MC passing this selection is displayed in Fig.~\ref{fig:dilepton_njets}. |
| 271 |
+ |
%We use this distribution to derive scale factors which reweight the \ttll\ MC \njets\ distribution to match the data. We define the following |
| 272 |
+ |
%quantities |
| 273 |
+ |
% |
| 274 |
+ |
%\begin{itemize} |
| 275 |
+ |
%\item $N_{2}=$ data yield minus non-dilepton \ttbar\ MC yield for \njets\ $\leq$ 2 |
| 276 |
+ |
%\item $N_{3}=$ data yield minus non-dilepton \ttbar\ MC yield for \njets\ = 3 |
| 277 |
+ |
%\item $N_{4}=$ data yield minus non-dilepton \ttbar\ MC yield for \njets\ $\geq$ 4 |
| 278 |
+ |
%\item $M_{2}=$ dilepton \ttbar\ MC yield for \njets\ $\leq$ 2 |
| 279 |
+ |
%\item $M_{3}=$ dilepton \ttbar\ MC yield for \njets\ = 3 |
| 280 |
+ |
%\item $M_{4}=$ dilepton \ttbar\ MC yield for \njets\ $\geq$ 4 |
| 281 |
+ |
%\end{itemize} |
| 282 |
+ |
% |
| 283 |
+ |
%We use these yields to define 3 scale factors, which quantify the data/MC ratio in the 3 \njets\ bins: |
| 284 |
+ |
% |
| 285 |
+ |
%\begin{itemize} |
| 286 |
+ |
%\item $SF_2 = N_2 / M_2$ |
| 287 |
+ |
%\item $SF_3 = N_3 / M_3$ |
| 288 |
+ |
%\item $SF_4 = N_4 / M_4$ |
| 289 |
+ |
%\end{itemize} |
| 290 |
+ |
% |
| 291 |
+ |
%And finally, we define the scale factors $K_3$ and $K_4$: |
| 292 |
+ |
% |
| 293 |
+ |
%\begin{itemize} |
| 294 |
+ |
%\item $K_3 = SF_3 / SF_2$ |
| 295 |
+ |
%\item $K_4 = SF_4 / SF_2$ |
| 296 |
+ |
%\end{itemize} |
| 297 |
+ |
% |
| 298 |
+ |
%The scale factor $K_3$ is extracted from dilepton \ttbar\ events with \njets = 3, which have exactly 1 ISR jet. |
| 299 |
+ |
%The scale factor $K_4$ is extracted from dilepton \ttbar\ events with \njets $\geq$ 4, which have at least 2 ISR jets. |
| 300 |
+ |
%Both of these scale factors are needed since dilepton \ttbar\ events which fall in our signal region (including |
| 301 |
+ |
%the \njets $\geq$ 4 requirement) may require exactly 1 ISR jet, in the case that the second lepton is reconstructed |
| 302 |
+ |
%as a jet, or at least 2 ISR jets, in the case that the second lepton is not reconstructed as a jet. These scale |
| 303 |
+ |
%factors are applied to the dilepton \ttbar\ MC only. For a given MC event, we determine whether to use $K_3$ or $K_4$ |
| 304 |
+ |
%by counting the number of reconstructed jets in the event ($N_{\rm{jets}}^R$) , and subtracting off any reconstructed |
| 305 |
+ |
%jet which is matched to the second lepton at generator level ($N_{\rm{jets}}^\ell$); $N_{\rm{jets}}^{\rm{cor}} = N_{\rm{jets}}^R - N_{\rm{jets}}^\ell$. |
| 306 |
+ |
%For events with $N_{\rm{jets}}^{\rm{cor}}=3$ the factor $K_3$ is applied, while for events with $N_{\rm{jets}}^{\rm{cor}}\geq4$ the factor $K_4$ is applied. |
| 307 |
+ |
%For all subsequent steps, the scale factors $K_3$ and $K_4$ have been |
| 308 |
+ |
%applied to the \ttll\ MC. |
| 309 |
+ |
|
| 310 |
+ |
|
| 311 |
+ |
Table~\ref{tab:njetskfactors} shows scale factors to correct the |
| 312 |
+ |
fraction of events with additional jets in MC to the observed fraction |
| 313 |
+ |
in data. These are applied to the \ttll\ MC throughout the entire analysis, i.e. whenever \ttll\ MC is used to estimate or subtract |
| 314 |
+ |
a yield or distribution. |
| 315 |
+ |
% |
| 316 |
+ |
In order to do so, it is first necessary to count the number of |
| 317 |
+ |
additional jets from radiation and exclude leptons mis-identified as |
| 318 |
+ |
jets. A jet is considered a mis-identified lepton if it is matched to a |
| 319 |
+ |
generator-level second lepton with sufficient energy to satisfy the jet |
| 320 |
+ |
\pt\ requirement ($\pt>30~\GeV$). |
| 321 |
+ |
|
| 322 |
+ |
\begin{table}[!ht] |
| 323 |
+ |
\begin{center} |
| 324 |
+ |
\begin{tabular}{l|c} |
| 325 |
+ |
\hline |
| 326 |
+ |
Jet Multiplicity Sample |
| 327 |
+ |
& Data/MC Scale Factor \\ |
| 328 |
+ |
\hline |
| 329 |
+ |
\hline |
| 330 |
+ |
N jets $= 3$ (sensitive to $\ttbar+1$ extra jet from radiation) & $0.97 \pm 0.03$\\ |
| 331 |
+ |
N jets $\ge4$ (sensitive to $\ttbar+\ge2$ extra jets from radiation) & $0.91 \pm 0.04$\\ |
| 332 |
+ |
\hline |
| 333 |
+ |
\end{tabular} |
| 334 |
+ |
\caption{Data/MC scale factors used to account for differences in the |
| 335 |
+ |
fraction of events with additional hard jets from radiation in |
| 336 |
+ |
\ttll\ events. \label{tab:njetskfactors}} |
| 337 |
+ |
\end{center} |
| 338 |
+ |
\end{table} |
| 339 |
+ |
|
| 340 |
+ |
|
| 341 |
+ |
\begin{figure}[hbt] |
| 342 |
+ |
\begin{center} |
| 343 |
+ |
\includegraphics[width=0.5\linewidth]{plots/ttdl_njets_lepremoval_comp.png} |
| 344 |
+ |
\caption{ |
| 345 |
+ |
\label{fig:dileptonnjets_lepcomp}%\protect |
| 346 |
+ |
Comparison of the jet multiplicity distribution for \ttll\ |
| 347 |
+ |
events in MC in the signal sample before (red) and after |
| 348 |
+ |
(blue) applying the lepton-jet overlap removal. Note only |
| 349 |
+ |
the first 6 jets are shown.} |
| 350 |
+ |
\end{center} |
| 351 |
+ |
\end{figure} |
| 352 |
+ |
|
| 353 |
+ |
|
| 354 |
+ |
In the signal sample, leptons mis-identified as jets are not rare. |
| 355 |
+ |
Figure~\ref{fig:dileptonnjets_lepcomp} shows the MC jet |
| 356 |
+ |
multiplicity distribution for \ttll\ events satisfying the full |
| 357 |
+ |
selection criteria before and after subtracting leptons mis-identified |
| 358 |
+ |
as jets. Approximately a quarter of the sample is comprised of 4-jet |
| 359 |
+ |
events that actually correspond to a 2-lepton + 3 jet event where the second |
| 360 |
+ |
lepton is counted as a jet. Lepton mis-identification depends strongly |
| 361 |
+ |
on the type of second lepton, occuring more frequently in the case of |
| 362 |
+ |
hadronic $\tau$s than leptonic objects. According to the \ttll\ |
| 363 |
+ |
MC, for hadronic $\tau$s, $\sim85\%$ of multi-prong $\tau$s and about half |
| 364 |
+ |
the single-prong $\tau$ are mis-identified as jets. In the case of |
| 365 |
+ |
leptonic objects, the fractions are smaller, comprising about a third |
| 366 |
+ |
of \E/\M\ from a \W\ decay and $<20\%$ for leptonic $\tau$s, |
| 367 |
+ |
mainly because of the softness of the decay products. |
| 368 |
+ |
The scale factors listed in Table.~\ref{tab:njetskfactors} are applied |
| 369 |
+ |
to the ``cleaned'' jet counts in the signal sample (shown in blue in |
| 370 |
+ |
Figure~\ref{fig:dileptonnjets_lepcomp}). The impact of applying the |
| 371 |
+ |
jet multiplicity scale factors on the \ttll\ is about a $10\%$ reduction in the |
| 372 |
+ |
background prediction for the signal region. |
| 373 |
+ |
|
| 374 |
+ |
%\begin{itemize} |
| 375 |
+ |
%\item Hadronic ($\tau$) objects: most multi-prong $\tau$s and about |
| 376 |
+ |
% half single-prong $\tau$s |
| 377 |
+ |
%\item Leptonic objects: smaller fraction, |
| 378 |
+ |
%\end{itemize} |
| 379 |
+ |
%Fraction of various lepton types matched to a jet |
| 380 |
+ |
%multi-prong taus ⟹ 85% give additional 30 GeV jet |
| 381 |
+ |
%single-prong taus ⟹ ~50% give additional 30 GeV jet |
| 382 |
+ |
%leptonic taus ⟹ <20% give additional 30 GeV jet |
| 383 |
+ |
%e/mu⟹ ~40% give additional 30 GeV jet |
| 384 |
+ |
|
| 385 |
+ |
\begin{figure}[hbt] |
| 386 |
+ |
\begin{center} |
| 387 |
+ |
\includegraphics[width=0.5\linewidth]{plots/ttdl_njets_presel_3j_comp.png}% |
| 388 |
+ |
\includegraphics[width=0.5\linewidth]{plots/ttdl_njets_presel_4j_comp.png} |
| 389 |
+ |
\caption{ |
| 390 |
+ |
\label{fig:dileptonnjets_signalcontrol_comp}%\protect |
| 391 |
+ |
Comparison of the number of additional jets from radiation |
| 392 |
+ |
in the 3-jet (left) and $\ge4$-jet (right) bins for the control \ttll\ |
| 393 |
+ |
sample (with two reconstructed leptons) and the signal |
| 394 |
+ |
sample (with one reconstructed lepton). The distributions |
| 395 |
+ |
show good agreement, indicating that the usage of the |
| 396 |
+ |
reconstructed jet multiplicity in one sample to reweight the |
| 397 |
+ |
signal sample is indeed justified. {\bf Fix me: Is this before or after the isolated track veto?}} |
| 398 |
+ |
\end{center} |
| 399 |
+ |
\end{figure} |
| 400 |
+ |
|
| 401 |
+ |
Ultimately, the interesting quantity for reweighting is the number of |
| 402 |
+ |
additional hard jets from radiation and this information is accessed using the |
| 403 |
+ |
number of reconstructed |
| 404 |
+ |
jets. Figure~\ref{fig:dileptonnjets_signalcontrol_comp} |
| 405 |
+ |
demonstrates in MC that the \ttll\ control sample, i.e. when both leptons are reconstructed, |
| 406 |
+ |
can indeed be used to reweight the \ttll\ signal sample, i.e. when one lepton is missed. |
| 407 |
+ |
The figure compares the |
| 408 |
+ |
number of additional jets from truth matching probed by N |
| 409 |
+ |
reconstructed jets, in this case 3 and $\ge4$ jets. In order to do so, |
| 410 |
+ |
jets that are truth-matched to the top decay products (the b-quarks |
| 411 |
+ |
and additional leptons) are removed. The 3-jet distribution shows |
| 412 |
+ |
excellent agreement and the differences in the $\ge4$-jet distribution |
| 413 |
+ |
are at most $5\%$. The impact of possible differences in the |
| 414 |
+ |
underlying distribution of extra |
| 415 |
+ |
jets between the signal and control \ttll\ samples are estimated by |
| 416 |
+ |
varying the scale factor contributions by $10\%$ and calculating the |
| 417 |
+ |
change in the dilepton prediction. This effect is found to have a |
| 418 |
+ |
negligible impact on the prediction, well below $1\%$. |
| 419 |
+ |
|
| 420 |
+ |
Other effects that have been examined include the impact of |
| 421 |
+ |
additional jets from pileup that may bias the jet multiplicity |
| 422 |
+ |
distribution, which is found to be a negligible effect in this dataset. The |
| 423 |
+ |
impact of the non-\ttll\ background on the jet fraction scale factors |
| 424 |
+ |
has also been studied. In particular, given the large uncertainty on |
| 425 |
+ |
the $\dy+HF$ MC prediction, this component has been varied by a factor |
| 426 |
+ |
of 2 and the resulting change on the dilepton prediction is $<1\%$. As |
| 427 |
+ |
a result, the dominant source of uncertainty is the statistical |
| 428 |
+ |
uncertainty, primarily from the two-lepton control sample size, that |
| 429 |
+ |
corresponds to a $3\%$ uncertainty on the dilepton prediction. |
| 430 |
+ |
|
| 431 |
+ |
The scale factors for the fraction of additional jets in the dilepton |
| 432 |
+ |
sample are applied throughout the analysis. It may be noted that this |
| 433 |
+ |
scaling is also performed consistently for the alternative \ttbar\ |
| 434 |
+ |
samples, always reweighting the jet multiplicity distribution to the |
| 435 |
+ |
data in the \ttll\ control sample. In this way, effects truly |
| 436 |
+ |
arising from using different MC samples and settings can be examined, |
| 437 |
+ |
separately from issues related to the modeling of additional jets. |
| 438 |
+ |
|
| 439 |
+ |
\subsubsection{Efficiency Corrections} |
| 440 |
+ |
|
| 441 |
+ |
[TO BE UDPATED WITH T\&P STUDIES ON ID, TRIGGER ETC] |
| 442 |
+ |
|
| 443 |
+ |
|
| 444 |
+ |
\subsubsection{Dilepton control regions} |
| 445 |
+ |
|
| 446 |
+ |
We define a dilepton control region requiring two isolated leptons, $ee, e\mu$, or $\mu\mu$ to study the jet multiplicity in data and MC, and derive |
| 447 |
+ |
scale factors based on their consistency. This study is documented in Section~\ref{sec:jetmultiplicity}. |
| 448 |
+ |
|
| 449 |
+ |
In this region we require: |
| 450 |
+ |
\begin{itemize} |
| 451 |
+ |
\item dilepton triggers |
| 452 |
+ |
\item two leptons with $\pt > 20 \GeV$ that pass our lepton id and isolation |
| 453 |
+ |
\item $\met > 50 \GeV$ |
| 454 |
+ |
\item $\ge 1$ b-tag, SSV medium |
| 455 |
+ |
\end{itemize} |
| 456 |
+ |
|
| 457 |
+ |
This sample is only partially overlapping with the single lepton preselection as it requires the dilepton rather than the single lepton triggers, and |
| 458 |
+ |
differs in the $\pt$ requirement for the leading lepton. Table~\ref{tab:dileptonyield} shows the raw yields in data and MC prior to any corrections. |
| 459 |
+ |
|
| 460 |
+ |
\begin{table}[!h] |
| 461 |
+ |
\begin{center} |
| 462 |
+ |
\begin{tabular}{c|c} |
| 463 |
+ |
\hline |
| 464 |
+ |
\hline |
| 465 |
+ |
\end{tabular} |
| 466 |
+ |
\caption{ Raw Data and MC predictions without any corrections are shown for the dilepton control region. |
| 467 |
+ |
This region is used for correcting the jet multiplicity seen in MC to that in data. |
| 468 |
+ |
\label{tab:dileptonyield}} |
| 469 |
+ |
\end{center} |
| 470 |
+ |
\end{table} |
| 471 |
+ |
|
