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\section{Introduction}
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\label{sec:introduction}
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The study of multiple gauge-boson production at the TeV scale
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constitutes a unique opportunity to test the Standard Model of
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Electroweak interactions at the highest possible energies. The
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production of \WZ\ events in \pp\ collisions at the LHC will allow to
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probe triple gauge-boson couplings and therefore non-Abelian gauge
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symmetry of the Standard Model at energy scales never attained
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before. Any anomalies in these couplings with respect to their
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Standard Model expectations could hint to indirect manifestation of New
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Physics.
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In addition, multi-lepton final states of \WZ\ production constitute
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an important background in the search for New Physics, in particular
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Supersymmetry. A sound understanding of the \WZ\ production-process is
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of paramount importance in the first phase of the LHC data-taking
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before any discovery can be claimed. At the same time, deviations of
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\WZ\ production rates and differential cross sections from the
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Standard Model expectation could hint to the direct production of new
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heavy particles.
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This note presents the first results on the study of \WZ\ production
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based on a full simulation of the CMS detector. \WZ production in \pp\
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collisions at the LHC mainly proceeds through quark annihilation into
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an intermediate W boson, see Figure~\ref{fig:graph}. Cross section of
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about 32\,pb and 20\,pb are expected for the \Wp\Z\ and \Wm\Z\ final states,
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respectively~\cite{Haywood:1999qg}.
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Final states where the gauge bosons decay into electrons and muons are
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considered in this analysis: $\rm e^\pm \epem$, $\mu^\pm \epem$, $\rm
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e^\pm \mu^+\mu^-$ and $\mu^\pm \mu^+\mu^-$. These final states allow a
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clean identification of the signal. The competing background processes
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are the Standard Model production of gauge bosons and top quarks
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The structure of this note is the following: section~\ref{sec:gen}
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describes the signal and background modeling;
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section~\ref{sec:eventReconstruction} contains the technical
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information on the event triggering and reconstruction;
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section~\ref{sec:ana} details the analysis strategy and summarises the
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analysis yield; section~\ref{sec:systematics} discusses the evaluation
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of systematic uncertainties; section~\ref{sec:results} illustrates the
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results of this first study of multiple gauge-boson production at the
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LHC, with particular emphasis on \WZ\ observation in the early LHC
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data; section~\ref{sec:conclusions} summarises our procedure and
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findings.
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\begin{figure}[hbt]
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\begin{center}
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\scalebox{0.5}{\includegraphics{figs/DiBosonProd.eps}}
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\caption{Dominant spectator Feynman diagrams for \WZ
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production in $\proton\proton$ collisions. The
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\mbox{$\pp\to\W\Z$} reaction occurs mainly through the $s$-channel
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$\q\qbar^{\prime}$ amplitude (left diagram), involving the $WWZ$ triple
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gauge-boson coupling.}
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\label{fig:graph}
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\end{center}
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\end{figure}
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