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\section{Acceptance systematics} |
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\section{Acceptance and efficiency systematics} |
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\label{sec:systematics} |
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This is a search for new physics contributions to |
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evidence for a contribution beyond SM expectations. |
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Strictly speaking it is impossible to talk about |
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``acceptance systematics'' because these kinds of |
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``acceptance and efficiency systematics'' because these kinds of |
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systematics only apply to a well defined final state. |
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Nevertheless, we can at least make some qualitative |
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statements. |
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Nevertheless, we can make general statements about the |
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systematic uncertainties, including quantitative |
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estimates of the systematic uncertainties associated with |
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a few specific processes. Note that we have used Spring10 |
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MC for the studies of systematic uncertainties described in this section, |
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and we are currently checking if any of the reported values |
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change after switching to Fall10 MC. |
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The systematic uncertainty on the lepton acceptance consists |
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of two parts: the trigger efficiency uncertainty and the |
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ID and isolation of uncertainty. We discuss these in turn. |
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ID and isolation uncertainty. We discuss these in turn. |
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The trigger efficiency |
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for two leptons of $P_T>10$ GeV, with one lepton of |
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$P_T>20$ GeV is very high, except in some corners |
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of phase space, see Section~\ref{sec:trgEff}. |
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of phase space, see Section~\ref{sec:trgeffsum}. |
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We estimate the efficiency uncertainty to be a few percent, |
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mostly in the low $P_T$ region. |
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mostly in the low $P_T$ region. For $t\bar{t}$, LM0 and LM1 |
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we find trigger efficiency uncertainties of less than 1\%, evaluated |
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by taking the difference in yields in the signal region between |
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assuming 100\% trigger efficiency and using the trigger efficiency model. |
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% trigger efficiency uncertainties: ttbar 0.3%, LM0 0.6%, LM1 0.6% |
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\begin{figure}[tbh] |
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\begin{center} |
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\includegraphics[width=0.75\linewidth]{eff_11.png} |
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\includegraphics[width=1.0\linewidth]{ttdilD6T_eff_Dec02_38X.png} |
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\includegraphics[width=1.0\linewidth]{lm_eff_Dec02_38X.png} |
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\caption{\label{fig:effttbar}\protect |
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Identification and isolation efficiencies for |
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leptons from $t \to W \to \ell$ and |
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$t \to W \to \tau \to \ell$ in |
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$t\bar{t}$ events.} |
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Identification and isolation efficiencies for leptons from $t \to W \to \ell$ and |
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$t \to W \to \tau \to \ell$ in $t\bar{t}$ events (top). Isolation efficiency |
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for $t\bar{t}$, LM0 and LM1 (bottom).} |
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\end{center} |
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\end{figure} |
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\begin{table}[hbt] |
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\begin{center} |
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\caption{\label{tab:tagandprobe} Tag and probe results on $Z \to \ell \ell$ |
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on data and MC. We quote ID efficiency given isolation and |
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the isolation efficiency given ID. } |
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\begin{tabular}{|l||c|c|} |
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\hline |
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& Data T\&P & MC T\&P \\ |
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\hline |
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$\epsilon(id|iso)$ electrons & $0.925 \pm 0.007$ & $0.934 \pm 0.004$ \\ |
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$\epsilon(iso|id)$ electrons & $0.991 \pm 0.002$ & $0.987 \pm 0.002$ \\ |
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$\epsilon(id|iso)$ muons & $0.962 \pm 0.005$ & $0.984 \pm 0.002$ \\ |
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$\epsilon(iso|id)$ muons & $0.987 \pm 0.003$ & $0.982 \pm 0.002$ \\ |
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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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The ID efficiencies in MC are shown in |
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Figures~\ref{fig:effttbar} |
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for the leptons from $t \to W \to \ell$ and $t \to W \to \tau \to \ell$. |
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Tag and probe studies show that these are correct to about |
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{\color{red} xx\%. (We need to do tag-and-probe on the full sample, |
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see what we get, and write text accordingly).} |
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The isolation efficiency depends on the jet activity in |
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Tag and probe studies show that these are correct to about 2\%, |
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see Table~\ref{tab:tagandprobe}. |
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Note that the isolation efficiency depends on the jet activity in |
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the final state. For example, in MC we find that the |
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lepton isolation efficiency differs by $\approx 4\%$ |
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{\bf per lepton} between $Z$ events and $t\bar{t}$ events\cite{ref:top}. |
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%\noindent {\bf This figure should be cut off at 100 GeV, and |
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%the y-axis should be zero-suppressed} |
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Another significant source of systematic uncertainty is |
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associated with the jet and $\met$ energy scale. The impact |
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of this uncertainty is very final-state dependent. Final |
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states characterized by lots of hadronic activity and \met are much |
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of this uncertainty is final-state dependent. Final |
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states characterized by lots of hadronic activity and \met are |
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less sensitive than final states where the \met and SumJetPt |
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are typically close to the requirement. To be more quantitative, |
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we have used the method of Reference~\cite{ref:top} to evaluate |
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assuming a 5\% uncertainty to the hadronic energy scale in CMS. |
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For $t\bar{t}$ we find uncertainties of 8\% (baseline |
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selection) and 30\% (signal region D); for LM0 and LM1 we find |
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14\% and 6\% respectively for signal region D. |
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selection) and 27\% (signal region D); for LM0 and LM1 we find |
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14\% and 6\% respectively for signal region D. |
