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\section{Introduction}
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\label{sec:intro}
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In this note we describe a search for new physics in the 2010
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opposite sign isolated dilepton sample ($ee$, $e\mu$, and $\mu\mu$).
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The main source of
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isolated dileptons at CMS is Drell Yan and $t\bar{t}$.
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Here we concentrate on dileptons with invariant mass inconsistent
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with $Z \to ee$ and $Z \to \mu\mu$. Thus $t\bar{t}$ is the most
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important background. A separate search for new physics in the $Z$
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sample is described in a separate note\cite{ref:Ztemplates}.
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The search strategy is the following
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\begin{itemize}
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\item We start out with a pre-selection which is as close as
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possible to the published (or soon to be published) $t\bar{t}$
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dilepton analysis\cite{ref:top} (same lepton ID, same jet definitions,
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etc.). We do make a couple of substantive modifications:
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\begin{enumerate}
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\item The top analysis requires two leptons of $P_T > 20$ GeV.
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In this
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analysis we lower the requirement on the second lepton to $P_T > 10$
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GeV. This is motivated by our desire to maintain sensitivity to possible
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SUSY signals with relatively low $P_T$ leptons generated in the
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cascade decays of heavy objects.
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\item The top analysis requires at least two jets of $P_T > 30$
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GeV with \met $>30$ GeV ($ee$ and $e\mu$) or \met $>20$ GeV ($e \mu$).
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We tighten the \met cut to 50 GeV and we
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also require that the scalar sum of the $P_T$ of all jets with $P_T > 30$
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GeV be $> 100$ GeV. These requirements considerably
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reduce backgrounds to the $t\bar{t}$ sample, {\em e.g.}, backgrounds
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from Drell Yan and $W+$jets.
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\end{enumerate}
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\item The pre-selection consists mostly of $t\bar{t}$ events. We perform
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data $-$ Monte Carlo comparisons of kinematical distributions. Assuming
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reasonable agreeement for the bulk of $t\bar{t}$ we move on to a
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search for new physics in the tail of the $t\bar{t}$.
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\item Our prejudice is that new physics would manifest itself in an
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excess of events with high \met and significant hadronic activity.
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We define an a-priori search region by tightening the \met and
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hadronic activity requirements such that we expect of order 1\%
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of $t\bar{t}$ events to pass the selection (as predicted by Monte Carlo).
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\item We perform a counting experiment in the signal region. We compare
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observed yields with expectations from Monte Carlo and with two independent
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data driven techniques (see Section~\ref{sec:abcd} and~\ref{sec:victory}).
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\end{itemize}
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