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\section{Non $t\bar{t}$ Backgrounds} |
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\label{sec:othBG} |
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\subsection{Dilepton backgrounds from rare SM processes} |
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\label{sec:bgrare} |
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Backgrounds from divector bosons and single top |
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can be reliably estimated from Monte Carlo. |
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They are negligible compared to $t\bar{t}$. |
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\subsection{Drell Yan background} |
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\label{sec:dybg} |
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%Backgrounds from Drell Yan are also expected |
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%to be negligible from MC. However one always |
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Thus we estimate the number of Drell Yan events in region $D'$ to |
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be $0.36\pm 0.36$. |
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We also perform the DY estimate in the region $A'$. Here we find |
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$N^{A'}(ee+\mu\mu)=5$, $N^{A'}(e\mu)=0$, |
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$R^{D'}_{out/in}=0.50\pm0.43$ (stat.), giving an estimated |
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number of Drell Yan events in region $A'$ to |
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be $2.5 \pm 2.4$. |
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This Drell Yan method could also be used to estimate |
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the number of DY events in the signal region (region $D$). |
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However, there is not enough statistics in the Monte |
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Carlo to make a measurement of $R_{out/in}$ in region |
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$D$. In any case, no $Z \to \ell\ell$ candidates are |
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found in region $D$. |
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found in region $D$. |
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%\end{table} |
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\subsection{Background from ``fake'' leptons} |
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\label{sec:bgfake} |
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Finally, we can use the ``Fake Rate'' method\cite{ref:FR} |
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to predict |
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the number of events with one fake lepton. We select |
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associated with electron ID cuts applied in the trigger.} |
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We then weight each event passing the full selection |
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by FR/(1-FR) where FR is the ``fake rate'' for the |
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fakeable object. {\color{red} \bf The results are...} |
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fakeable object. |
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We first apply this method to events passing the preselection. |
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The raw result is $6.7 \pm 1.7 \pm 3.4$, where the first uncertainty is |
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statistical and the second uncertainty is from the 50\% systematic |
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uncertainty associated with this method\cite{ref:FR}. This has |
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to be corrected for ``signal contamination'', {\em i.e.}, the |
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contribution from true dilepton events with one lepton |
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failing the selection. This is estimated from Monte Carlo |
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to be $2.3 \pm 0.05$, where the uncertainty is from MC statistics |
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only. Thus, the estimates number of events with one ``fake'' |
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lepton after the preselection is $4.4 \pm 3.8$. |
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The Monte Carlo expectation for this contribution can be obtained |
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by summing up the $t\bar{t}\rightarrow \mathrm{other}$ and |
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$W^{\pm}$ + jets entries from Table~\ref{tab:yields}. This |
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result is $2.0 \pm 0.2$ (stat. error only). Thus, this study |
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confirms that the contribution of fake leptons to the event sample |
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after preselection is small, and consistent with the MC prediction. |
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We apply the same method to events in the signal region (region D). |
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There are no events where one of the leptons passes the full selection and |
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the other one fails the full selection but passes the |
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``Fakeable Object'' selection. Thus the background estimate |
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is $0.0^{+0.4}_{-0.0}$, where the upper uncertainty corresponds (roughly) |
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to what we would have calculated if we had found one such event. |
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We can also apply a similar technique to estimate backgrounds |
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with two fake leptons, {\em e.g.}, from QCD events. |
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In this case we select events with both |
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leptons failing the full selection but passing the |
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``Fakeable Object'' selection. For the preselection, the |
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result is $0.2 \pm 0.2 \pm 0.2$, where the first uncertainty |
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is statistical and the second uncertainty is from the fake rate |
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systematics (50\% per lepton, 100\% total). Note that this |
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double fake contribution is already included in the $4.4 \pm 3.8$ |
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single fake estimate discussed above $-$ in fact, it is double counted. |
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Therefore the total fake estimate is $4.0 \pm 3.8$ (single fakes) |
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and $0.2 \pm 0.2 \pm 0.2$ (double fakes). |
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{\color{red} \bf We will do the same thing that we did for |
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the top analysis, but we will only do it on the full dataset.} |
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In the signal region (region D), the estimated double fake background |
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is $0.00^{+0.04}_{-0.00}$. This is negligible. |
