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\section{Introduction}
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\label{sec:intro}
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In this note we describe a first study of isolated same sign (SS)
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and opposite sign (OS) low $P_T$ ($P_T > 10$ GeV)
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dileptons (e or $\mu$)
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in 7 TeV collision data. Our goal is to understand this
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data sample as a first step towards a top cross-section
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analysis~\cite{ref:topdil2009}, a $WW$ cross-section
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analysis~\cite{ref:WW}, as well as SS and OS SUSY
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searches\cite{ref:OSSusy}\cite{ref:SSSusy}.
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With a 10 GeV $P_T$ threshold, the data sample is dominated by QCD
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backgrounds and Drell-Yan events. We compare the observed yields
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with predictions from Monte Carlo. In the case of QCD, we use
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the Fake Rate method to predict its rate in a data driven way.
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With the present luminosity, there is not enough statistics to
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study kinematical distributions.
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This note is organized as follows. In Section~\ref{sec:datasets}
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we list the datasets used; the lepton identification criteria
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and the general event selection requirements
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are given in Section~\ref{sec:selection}; the event data yields are
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compared with Monte Carlo expectations in Section~\ref{sec:yields};
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the FR method is reviewed in Section~\ref{sec:FR}; the FR is tested
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in an enriched Heavy Flavor sample in Section~\ref{sec:btag};
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finally, the application
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of the FR method to the dilepton sample
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is summarized in Section~\ref{sec:FRapply}.
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{\color{blue} This document was originally based on $\approx$ 10
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nb$^{-1}$ of integrated luminosity. It has now been partially
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updated to higher luminosity for ICHEP. We only update the
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SS sign results becuse these are the ones that are relevant
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for the SUSY ICHEP PAS (SUS-10-001). Furthermore the OS results are
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less relevant for the ``Fake Rate'' studies because of the
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large Drell-Yan contribution. A more complete study of the
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OS sample is documented in our top-dilepton analysis note (AN 2010-193)
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and the top ICHEP PAS (TOP-10-04).
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Following instructions
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from the SUSY convenors, we leave the old results in the
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document. To facilitate reading, the document is color coded:
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\begin{itemize}
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\item everything in blue is new
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\item everything in {\color{red}red} is old information that has been updated
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\item everything in {\color{black}black} is old information that has not
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been updated. In the case of plots and results, these would still be
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with the $\approx$ 10 nb$^{-1}$.
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\end{itemize}
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} |
