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\section{Introduction} |
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\label{sec:introduction} |
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– |
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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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|
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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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constitutes a unique opportunity to test the standard model of |
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electroweak interactions at the highest possible energies. |
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The production of \WZ\ events in \pp\ collisions at the LHC allows 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 energies never attained |
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before. Any deviation of the strength of these couplings from |
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their standard model expectations manifests the new physics. |
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|
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In addition, multi-lepton final states of \WZ\ production constitutes |
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an important background to potential new phenomena, |
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in particular Supersymmetry. A good understanding of the \WZ\ |
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production-process is of paramount importance in the first phase |
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of the LHC data-taking before any discovery can be claimed. |
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At the same time, deviation of the \WZ\ production rate and |
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differential cross sections from the standard model predictions |
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could hint to the direct production of new 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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In this note, we present results on the study of \WZ\ production |
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based on the 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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an intermediate W boson, see Fig.~\ref{fig:graph}. Cross section of |
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about 31 pb and 19 pb are expected for the $W^+\Z$ and $W^-\Z$ final states, |
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respectively~\cite{Haywood:1999qg}. There are four configuration of |
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final state leptons considered in this analysis: $e^\pm \epem$, |
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$\mu^\pm \epem$, $\rm e^\pm \mu^+\mu^-$, and $\mu^\pm \mu^+\mu^-$. |
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Main instrumental background to all of the four signatures is due to |
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misidentified jets from top quark production and associative \Z or \W boson |
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and jets production. Next in significance is a background from |
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converted photons from $Z^0\gamma$ and $\W\gamma$ processes |
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that are identified as electrons. The only physics background to \WZ\ final state is $\Z\Z$ |
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production with one of the leptons being mis-reconstructed or lost. |
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The structure of this note is as follows. We describe the signal |
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and background modeling in Section~\ref{sec:gen}. The information |
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on triggering and reconstruction of events is given in |
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Section~\ref{sec:eventReconstruction}. We present the methods of measuring |
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signal and background yields and estimate systematic uncertainties in |
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Sections~\ref{sec:SignalExt} and~\ref{sec:systematic}, respectively. |
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The summary of the analysis and results drawn with an emphasis on the |
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\WZ\ observation in early LHC data are given in Section~\ref{sec:results}. |
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\begin{figure}[hbt] |
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\begin{center} |
