| 1 |
vuko |
1.1 |
|
| 2 |
|
|
\section{Introduction}
|
| 3 |
|
|
\label{sec:introduction}
|
| 4 |
|
|
|
| 5 |
|
|
|
| 6 |
|
|
The study of multiple gauge-boson production at the TeV scale
|
| 7 |
|
|
constitutes a unique opportunity to test the Standard Model of
|
| 8 |
|
|
Electroweak interactions at the highest possible energies. The
|
| 9 |
|
|
production of \WZ\ events in \pp\ collisions at the LHC will allow to
|
| 10 |
|
|
probe triple gauge-boson couplings and therefore non-Abelian gauge
|
| 11 |
|
|
symmetry of the Standard Model at energy scales never attained
|
| 12 |
|
|
before. Any anomalies in these couplings with respect to their
|
| 13 |
|
|
Standard Model expectations could hint to indirect manifestation of New
|
| 14 |
|
|
Physics.
|
| 15 |
|
|
|
| 16 |
|
|
In addition, multi-lepton final states of \WZ\ production constitute
|
| 17 |
|
|
an important background in the search for New Physics, in particular
|
| 18 |
|
|
Supersymmetry. A sound understanding of the \WZ\ production-process is
|
| 19 |
|
|
of paramount importance in the first phase of the LHC data-taking
|
| 20 |
|
|
before any discovery can be claimed. At the same time, deviations of
|
| 21 |
|
|
\WZ\ production rates and differential cross sections from the
|
| 22 |
|
|
Standard Model expectation could hint to the direct production of new
|
| 23 |
|
|
heavy particles.
|
| 24 |
|
|
|
| 25 |
|
|
This note presents the first results on the study of \WZ\ production
|
| 26 |
|
|
based on a full simulation of the CMS detector. \WZ production in \pp\
|
| 27 |
|
|
collisions at the LHC mainly proceeds through quark annihilation into
|
| 28 |
|
|
an intermediate W boson, see Figure~\ref{fig:graph}. Cross section of
|
| 29 |
|
|
about 32\,pb and 20\,pb are expected for the \Wp\Z\ and \Wm\Z\ final states,
|
| 30 |
|
|
respectively~\cite{Haywood:1999qg}.
|
| 31 |
|
|
|
| 32 |
|
|
Final states where the gauge bosons decay into electrons and muons are
|
| 33 |
|
|
considered in this analysis: $\rm e^\pm \epem$, $\mu^\pm \epem$, $\rm
|
| 34 |
|
|
e^\pm \mu^+\mu^-$ and $\mu^\pm \mu^+\mu^-$. These final states allow a
|
| 35 |
|
|
clean identification of the signal. The competing background processes
|
| 36 |
|
|
are the Standard Model production of gauge bosons and top quarks
|
| 37 |
|
|
|
| 38 |
|
|
The structure of this note is the following: section~\ref{sec:gen}
|
| 39 |
|
|
describes the signal and background modeling;
|
| 40 |
|
|
section~\ref{sec:eventReconstruction} contains the technical
|
| 41 |
|
|
information on the event triggering and reconstruction;
|
| 42 |
|
|
section~\ref{sec:ana} details the analysis strategy and summarises the
|
| 43 |
|
|
analysis yield; section~\ref{sec:systematics} discusses the evaluation
|
| 44 |
|
|
of systematic uncertainties; section~\ref{sec:results} illustrates the
|
| 45 |
|
|
results of this first study of multiple gauge-boson production at the
|
| 46 |
|
|
LHC, with particular emphasis on \WZ\ observation in the early LHC
|
| 47 |
|
|
data; section~\ref{sec:conclusions} summarises our procedure and
|
| 48 |
|
|
findings.
|
| 49 |
|
|
|
| 50 |
|
|
\begin{figure}[hbt]
|
| 51 |
|
|
\begin{center}
|
| 52 |
|
|
\scalebox{0.5}{\includegraphics{figs/DiBosonProd.eps}}
|
| 53 |
|
|
\caption{Dominant spectator Feynman diagrams for \WZ
|
| 54 |
|
|
production in $\proton\proton$ collisions. The
|
| 55 |
|
|
\mbox{$\pp\to\W\Z$} reaction occurs mainly through the $s$-channel
|
| 56 |
|
|
$\q\qbar^{\prime}$ amplitude (left diagram), involving the $WWZ$ triple
|
| 57 |
|
|
gauge-boson coupling.}
|
| 58 |
|
|
\label{fig:graph}
|
| 59 |
|
|
\end{center}
|
| 60 |
|
|
\end{figure}
|
