claudioc/dilNoteICHEP/introduction.tex

\section{Introduction}
\label{sec:intro}

In this note we describe a first study of isolated same sign (SS)
and opposite sign (OS) low $P_T$ ($P_T > 10$ GeV)
dileptons (e or $\mu$) 
in 7 TeV collision data.  Our goal is to understand this 
data sample as a first step towards a top cross-section
analysis~\cite{ref:topdil2009}, a $WW$ cross-section 
analysis~\cite{ref:WW}, as well as SS and OS SUSY 
searches\cite{ref:OSSusy}\cite{ref:SSSusy}.  

With a 10 GeV $P_T$ threshold, the data sample is dominated by QCD 
backgrounds and Drell-Yan events.  We compare the observed yields
with predictions from Monte Carlo.  In the case of QCD, we use
the Fake Rate method to predict its rate in a data driven way.
With the present luminosity, there is not enough statistics to
study kinematical distributions.

This note is organized as follows.  In Section~\ref{sec:datasets} 
we list the datasets used; the lepton identification criteria 
and the general event selection requirements 
are given in Section~\ref{sec:selection}; the event data yields are
compared with Monte Carlo expectations in Section~\ref{sec:yields};
the FR method is reviewed in Section~\ref{sec:FR};  the FR is tested
in an enriched Heavy Flavor sample in Section~\ref{sec:btag};
finally, the application
of the FR method to the dilepton sample 
is summarized in Section~\ref{sec:FRapply}.

{\color{blue} This document was originally based on $\approx$ 10
nb$^{-1}$ of integrated luminosity.  It has now been partially 
updated to higher luminosity for ICHEP.  We only update the 
SS sign results becuse these are the ones that are relevant
for the SUSY ICHEP PAS (SUS-10-001).  Furthermore the OS results are
less relevant for the ``Fake Rate'' studies because of the 
large Drell-Yan contribution.  A more complete study of the
OS sample is documented in our top-dilepton analysis note (AN 2010-193)
and the top ICHEP PAS (TOP-10-04).

Following instructions
from the SUSY convenors, we leave the old results in the
document.  To facilitate reading, the document is color coded:
\begin{itemize}
\item everything in blue is new
\item everything in {\color{red}red} is old information that has been updated
\item everything in {\color{black}black} is old information that has not 
been updated.  In the case of plots and results, these would still be 
with the $\approx$ 10 nb$^{-1}$.
\end{itemize}
}
Revision:	1.5
Committed:	Fri Jul 9 09:33:21 2010 UTC (14 years, 10 months ago) by claudioc
Content type:	application/x-tex
Branch:	MAIN
CVS Tags:	v8, HEAD
Changes since 1.4:	+5 -2 lines
Log Message:	misc. + asymmetric errors
#	User	Rev	Content
1	claudioc	1.1	\section{Introduction}
2			\label{sec:intro}
3
4			In this note we describe a first study of isolated same sign (SS)
5			and opposite sign (OS) low $P_T$ ($P_T > 10$ GeV)
6			dileptons (e or $\mu$)
7			in 7 TeV collision data. Our goal is to understand this
8			data sample as a first step towards a top cross-section
9			analysis~\cite{ref:topdil2009}, a $WW$ cross-section
10			analysis~\cite{ref:WW}, as well as SS and OS SUSY
11			searches\cite{ref:OSSusy}\cite{ref:SSSusy}.
12
13			With a 10 GeV $P_T$ threshold, the data sample is dominated by QCD
14			backgrounds and Drell-Yan events. We compare the observed yields
15			with predictions from Monte Carlo. In the case of QCD, we use
16			the Fake Rate method to predict its rate in a data driven way.
17			With the present luminosity, there is not enough statistics to
18			study kinematical distributions.
19
20			This note is organized as follows. In Section~\ref{sec:datasets}
21			we list the datasets used; the lepton identification criteria
22			and the general event selection requirements
23			are given in Section~\ref{sec:selection}; the event data yields are
24			compared with Monte Carlo expectations in Section~\ref{sec:yields};
25	claudioc	1.5	the FR method is reviewed in Section~\ref{sec:FR}; the FR is tested
26			in an enriched Heavy Flavor sample in Section~\ref{sec:btag};
27			finally, the application
28			of the FR method to the dilepton sample
29			is summarized in Section~\ref{sec:FRapply}.
30	claudioc	1.1
31	claudioc	1.3	{\color{blue} This document was originally based on $\approx$ 10
32	claudioc	1.2	nb$^{-1}$ of integrated luminosity. It has now been partially
33	claudioc	1.4	updated to higher luminosity for ICHEP. We only update the
34			SS sign results becuse these are the ones that are relevant
35			for the SUSY ICHEP PAS (SUS-10-001). Furthermore the OS results are
36			less relevant for the ``Fake Rate'' studies because of the
37			large Drell-Yan contribution. A more complete study of the
38			OS sample is documented in our top-dilepton analysis note (AN 2010-193)
39			and the top ICHEP PAS (TOP-10-04).
40
41			Following instructions
42	claudioc	1.2	from the SUSY convenors, we leave the old results in the
43			document. To facilitate reading, the document is color coded:
44			\begin{itemize}
45	claudioc	1.3	\item everything in blue is new
46			\item everything in {\color{red}red} is old information that has been updated
47	claudioc	1.2	\item everything in {\color{black}black} is old information that has not
48			been updated. In the case of plots and results, these would still be
49			with the $\approx$ 10 nb$^{-1}$.
50			\end{itemize}
51			}