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\section{Event Yields}
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\label{sec:yields}
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In this Section we compare the event yields in SS and OS with
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the MC predictions. The MC predictions are normalized to
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the data integrated luminosity (Section~\ref{sec:lumi}),
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and are broken down into contributions
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from QCD, $\gamma +$ jets, and Drell-Yan. The integrated
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luminosity of the lowest $P_T$ QCD bin (QCDPt15) is only
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$\approx$ 7 nb$^{-1}$,
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which is smaller than the integrated luminosity of the data.
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Thus we have ``stitched'' together the QCDPt15 and QCDPt30
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MC samples by requiring $\hat{P}_T < 30$ for the
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QCDPt15 sample. Even so, the QCD statistics are not sufficient
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for a meaningful comparison.
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The event yields in data and Monte Carlo for SS and
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OS are given in
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Tables~\ref{tab:yieldOS} and~{\color{red}\ref{tab:yieldSS} (old)} as well as~
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{\color{blue}\ref{tab:yieldSS2} (updated).}
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\begin{table}[htb]
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\begin{center}
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\caption{\label{tab:yieldOS} Observed and MC-predicted yields in the OS
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selection. Quoted uncertainties are MC statistics only. In case that
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no QCDPt15 MC event passes the selection, we quote the uncertainty as the weight
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of one QCDPt15 MC event.}
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\begin{tabular}{|l|c|c|c|c|c|} \hline
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Final State & QCD & $\gamma +$ jet & DY & Total MC & Data \\
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\hline
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ee & 0$\pm$2 & 0.01 $\pm$ 0.004 & 0.83$\pm$0.02 & 0.84$\pm$2.0 & 2 \\
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e$\mu$ & 0.17$\pm$2 & 0.000$\pm$0.004 & 0.08 $\pm$ 0.01& 0.25$\pm$2.0 & 0 \\
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$\mu\mu$& 0$\pm$2 & 0 & 1.36$\pm$0.03 &1.36$\pm$2.0& 3 \\
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\hline
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All &0.17$\pm$3 &0.01$\pm$0.004 & 2.27$\pm$0.03 & 2.44$\pm$3.0 & 5 \\
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\hline
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\end{tabular}
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\end{center}
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\end{table}
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\begin{table}[htb]
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\begin{center}
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{\color{red}
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\caption{\label{tab:yieldSS} Observed and MC-predicted yields in the SS
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selection. Quoted uncertainties are MC statistics only. In case that
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no QCDPt15 MC event passes the selection, we quote the uncertainty as the weight
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of one QCDPt15 MC event.(Old Table which is updated below)}
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\begin{tabular}{|l|c|c|c|c|c|} \hline
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Final State & QCD & $\gamma +$ jet & DY & Total MC & Data \\
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\hline
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ee & $0 \pm 2$ & $0.002 \pm 0.002$ & $0.01 \pm 0.003$&$ 0.01\pm 2.0$ &0 \\
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e$\mu$ & $0 \pm 2$ & $0.004 \pm 0.003$ & $0.005 \pm 0.002$&$ 0.01 \pm 2.0 $ &0 \\
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$\mu\mu$ & $0 \pm 2$ & 0 & $0.001 \pm 0.001$&$ 0.001\pm 2.0 $ &0 \\
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\hline
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All & $0 \pm 3$ & $0.006 \pm 0.003$ & $0.016 \pm 0.003$&$0.02\pm 3.0 $ &0 \\
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\hline
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\end{tabular}
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}
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\end{center}
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\end{table}
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\begin{table}[htb]
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\begin{center}
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{\color{blue}
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\caption{\label{tab:yieldSS2} Observed and MC-predicted yields in the SS
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selection. Quoted uncertainties are MC statistics only. In case that
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no QCDPt15 MC event passes the selection, we quote the uncertainty as the weight
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of one QCDPt15 MC event. (New updated Table)}
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\begin{tabular}{|l|c|c|c|c|c|} \hline
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Final State & QCD & $\gamma +$ jet & DY & Total MC & Data \\
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\hline
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ee & $0 \pm 11$ & $0.01 \pm 0.01$ & $0.07 \pm 0.01$&$ 0.08\pm 11$ &0 \\
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e$\mu$ & $0 \pm 11$ & $0.02 \pm 0.01$ & $0.02 \pm 0.01$&$ 0.04 \pm 11 $ &1 \\
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$\mu\mu$ & $0 \pm 11$ & 0 & $0.01 \pm 0.04$&$ 0.01\pm 11 $ &0 \\
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\hline
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All & $0 \pm 19$ & $0.03 \pm 0.02$ & $0.10 \pm 0.02$&$0.13\pm 19 $ &1 \\
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\hline
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\end{tabular}
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}
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\end{center}
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\end{table}
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We find the $\gamma +$ jet MC predictions to be negligible.
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The QCD statistics are so poor that we cannot make any quantitative
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statement.
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The OS data is dominated by Drell Yan. The agreement between
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MC and data yields is good.
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For now we use the MC to predict the rate of SS events from Drell-Yan
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off the $Z$ peak. These events are mostly from electron charge misidentification.
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We have developed techniques to measure this charge flip probability
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from $Z \to ee$ data\cite{ref:SSSusy}. However, this cannot be done at the
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present level of statistics. Interestingly enough, we did find one SS
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$e^+e^+$ event that is removed by the $Z$-mass
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cut. We believe this to be a $Z \to e^+e^-$ event with one
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charge misassignment\cite{ref:HN}.
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