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\section{Event Preselection}
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\label{sec:eventSel}
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{\color{red} This needs to be fixed up -- probably many mistakes present.}\\
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As mentioned in the introduction, the preselection is based on the
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$t\bar{t}$ analysis. We select events with two opposite sign isolated
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leptons ($ee$, $e\mu$, or $\mu\mu$); one of the leptons must
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have $P_T > 20$ GeV,
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the other one must have $P_T > 10$ GeV; there must be two JPT
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jets of $P_T > 30$ GeV and $|\eta| <$ {\color{red} xx}; the scalar sum of the
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$P_T$ of all such jets must exceed 100 GeV; finally $\met > 50$ GeV
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(we use tcMet). More details are given in the subsection below.
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\subsection{Event Cleanup}
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\label{sec:cleanup}
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\begin{itemize}
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\item Scraping cut: if there are $\geq$ 10 tracks, require at
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least 25\% of them to be high purity.
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\item Require at least one good vertex:
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\begin{itemize}
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\item not fake
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\item ndof $>$ 4
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\item $|\rho| < 2$ cm
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\item $|z| < 24$ cm.
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\end{itemize}
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\end{itemize}
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\subsection{Muon Selection}
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\label{sec:muon}
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Muon candidates are RECO muon objects passing the following
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requirements:
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\begin{itemize}
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\item $|\eta| < 2.5$.
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\item Global Muon and Tracker Muon.
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\item $\chi^2$/ndof of global fit $<$ 10.
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\item At least 11 hits in the tracker fit.
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\item Transverse impact parameter with respect to the beamspot $<$ 200 $\mu$m.
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\item $Iso \equiv $ $E_T^{\rm iso}$/Max(20 GeV, $P_T$) $<$ 0.15.
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$E_T^{\rm iso}$
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is defined as the sum of transverse energy/momentum deposits in ecal,
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hcal, and tracker, in a cone of 0.3.
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\item At least one of the hits from the
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standalone muon must be used in the global fit.
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\end{itemize}
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\subsection{Electron Selection}
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\label{sec:electron}
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Electron candidates are RECO GSF electrons passing the following
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requirements:
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\begin{itemize}
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\item $P_T > 10$ GeV. (The $t\bar{t}$ analysis uses 20 GeV but for
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completeness we calculate FR down to 10 GeV).
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\item $|\eta| < 2.5$.
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\item SuperCluster $E_T > 10$ GeV.
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\item The electron must be ecal seeded.
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\item VBTF90 identification\cite{ref:vbtf}.
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\item Transverse impact parameter with respect to the beamspot $<$ 400 $\mu$m.
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\item $Iso \equiv $ $E_T^{\rm iso}$/Max(20 GeV, $P_T$) $<$ 0.15.
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$E_T^{\rm iso}$
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is defined as the sum of transverse energy/momentum deposits in ecal,
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hcal, and tracker, in a
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cone of 0.3. A 1 GeV pedestal is subtracted from the ecal energy
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deposition in the EB, however the ecal energy is never allowed to
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go negative.
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\item Electrons with a tracker or global muon within $\Delta R$ of
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0.1 are vetoed.
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\item The number of missing expected inner hits must be less than
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two\cite{ref:conv}.
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\item Conversion removal via partner track finding: any electron
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where an additional GeneralTrack is found with $Dist < 0.02$ cm
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and $\Delta \cot \theta < 0.02$ is vetoed\cite{ref:conv}.
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\item Cleaning for ECAL spike (aka Swiss-Cross cleaning) has been applied
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at the reconstruction level (CMSSW 38x).
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\end{itemize}
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\subsection{Z veto}
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\label{sec:zveto}
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We remove $e^+e^-$ and $\mu^+ \mu^-$ events with invariant
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mass between 76 and 106 GeV.
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\subsection{Trigger Selection}
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\label{sec:trigSel}
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Because most of the triggers implemented in the 2nd half of the
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2010 run were not implemented in the Monte Carlo, no trigger
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selection is applied on Monte Carlo data. As discussed in
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Section~\ref{sec:trgEff}, a trigger efficiency weight is applied
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to each event, based on the trigger efficiencies measured on data.
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Trigger efficiency weights are very close to 1.
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For data, we require the logical OR of all (or most?) unprescaled
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single and double lepton triggers that were deployed during the 2010
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run. These are:
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{\color{red} Here we need to list the triggers, somehow.}
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