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\label{sec:datadriven} |
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We have developed two data-driven methods to |
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estimate the background in the signal region. |
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The first one explouts the fact that |
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The first one exploits the fact that |
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\met and \met$/\sqrt{\rm SumJetPt}$ are nearly |
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uncorrelated for the $t\bar{t}$ background |
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(Section~\ref{sec:abcd}); the second one |
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|
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|
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Monte Carlo studies give values of $K$ that are typically between 1.5 and 1.6, |
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depending on selection details. Given the integrated luminosity of the |
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present dataset, the determination of $K$ in data is severely statistics |
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limited. Thus, we take $K$ from $t\bar{t}$ Monte Carlo as |
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depending on selection details. |
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%%%TO BE REPLACED |
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%Given the integrated luminosity of the |
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%present dataset, the determination of $K$ in data is severely statistics |
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%limited. Thus, we take $K$ from $t\bar{t}$ Monte Carlo as |
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|
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%\begin{center} |
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%$ K_{MC} = \frac{\int_0^{\infty} {\cal N}(\met)~~d\met~}{\int_{50}^{\infty} {\cal N}(\met)~~d\met~}$ |
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%\end{center} |
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|
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\begin{center} |
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$ K_{MC} = \frac{\int_0^{\infty} {\cal N}(\met)~~d\met~}{\int_{50}^{\infty} {\cal N}(\met)~~d\met~}$ |
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\end{center} |
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|
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\noindent {\color{red} For the 11 pb result we have used $K$ from data.} |
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%\noindent {\color{red} For the 11 pb result we have used $K$ from data.} |
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|
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There are several effects that spoil the correspondance between \met and |
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$P_T(\ell\ell)$: |
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We have studied this effect at the generator level using Alpgen. We find |
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that the bias is at the few percent level. |
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|
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%%%TO BE REPLACED |
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%Based on the results of Table~\ref{tab:victorybad}, we conclude that the |
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%naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to |
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%be corrected by a factor of {\color{red} $ K_{\rm{fudge}} =1.2 \pm 0.3$ |
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%(We still need to settle on thie exact value of this. |
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%For the 11 pb analysis it is taken as =1.)} . The quoted |
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%uncertainty is based on the stability of the Monte Carlo tests under |
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%variations of event selections, choices of \met algorithm, etc. |
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%For example, we find that observed/predicted changes by roughly 0.1 |
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%for each 1.5\% change in the average \met response. |
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|
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Based on the results of Table~\ref{tab:victorybad}, we conclude that the |
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naive data driven background estimate based on $P_T{(\ell\ell)}$ needs to |
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be corrected by a factor of {\color{red} $ K_{\rm{fudge}} =1.2 \pm 0.3$ |
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(We still need to settle on thie exact value of this. |
| 201 |
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For the 11 pb analysis it is taken as =1.)} . The quoted |
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uncertainty is based on the stability of the Monte Carlo tests under |
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be corrected by a factor of $ K = X \pm Y$. |
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The value of this correction factor as well as the systematic uncertainty |
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will be assessed using 38X ttbar madgraph MC. In the following we use |
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$K = 1$ for simplicity. Based on previous MC studies we foresee a correction |
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factor of $\approx 1.2 - 1.4$, and we will assess an uncertainty |
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based on the stability of the Monte Carlo tests under |
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variations of event selections, choices of \met algorithm, etc. |
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For example, we find that observed/predicted changes by roughly 0.1 |
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for each 1.5\% change in the average \met response. |
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for each 1.5\% change in the average \met response. |
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|
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|
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|
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for the background predictions of the ABCD method including LM0 or |
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LM1. Results |
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are normalized to 30 pb$^{-1}$.} |
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\begin{tabular}{|c||c|c||c|c|} |
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\begin{tabular}{|c|c||c|c||c|c|} |
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\hline |
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SM & SM$+$LM0 & BG Prediction & SM$+$LM1 & BG Prediction \\ |
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Background & Contribution& Including LM0 & Contribution & Including LM1 \\ \hline |
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1.2 & 6.8 & 3.7 & 3.4 & 1.3 \\ |
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SM & BG Prediction & SM$+$LM0 & BG Prediction & SM$+$LM1 & BG Prediction \\ |
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Background & SM Only & Contribution & Including LM0 & Contribution & Including LM1 \\ \hline |
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1.2 & 1.0 & 6.8 & 3.7 & 3.4 & 1.3 \\ |
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\hline |
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\end{tabular} |
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\end{center} |
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for the background predictions of the $P_T(\ell\ell)$ method including LM0 or |
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LM1. Results |
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are normalized to 30 pb$^{-1}$.} |
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< |
\begin{tabular}{|c||c|c||c|c|} |
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> |
\begin{tabular}{|c|c||c|c||c|c|} |
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\hline |
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SM & SM$+$LM0 & BG Prediction & SM$+$LM1 & BG Prediction \\ |
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Background & Contribution& Including LM0 & Contribution & Including LM1 \\ \hline |
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1.2 & 6.8 & 2.2 & 3.4 & 1.5 \\ |
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SM & BG Prediction & SM$+$LM0 & BG Prediction & SM$+$LM1 & BG Prediction \\ |
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Background & SM Only & Contribution & Including LM0 & Contribution & Including LM1 \\ \hline |
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1.2 & 1.0 & 6.8 & 2.2 & 3.4 & 1.5 \\ |
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\hline |
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\end{tabular} |
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\end{center} |
