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\chapter{The \LHCb experiment}
\label{chap:MoreStuff}
\chapterquote{There, sir! that is the perfection of vessels!}
{Jules Verne, 1828--1905}
\section{The \LHC}
The Large Hadron Collider (\LHC) at \CERN is a new hadron collider,
located in the same tunnel as the Large Electron-Positron collider
(\LEP)~\cite{Brianti:2004qq}. Where \LEP's chief task was the use
of \unit{90--207}{\GeV} \epluseminus collisions to establish the
precision physics of electroweak unification\dots
\begin{figure}
\includegraphics[width=\largefigwidth]{ckmfitter-alpha-combined}
\caption[CKM Fitter constraints on \alphaCKM.]%
{CKM Fitter constraints on \alphaCKM from combined \BToPiPi,
\BToRhoPi and \BToRhoRho decay analyses.}
\label{fig:CKMFitter}
\end{figure}
\section{The \LHCb experiment}
\label{sec:LHCbInDetail}
Since both \bhadron{s} are preferentially produced in the same direction
and are forward-boosted along the beam-pipe, the detector is not required
to have full $4\pi$ solid-angle coverage. \LHCb takes advantage of this
by using a wedge-shaped single-arm detector with angular acceptance
\unit{10-300}{\mrad} in the horizontal (bending) plane~\cite{Amato:1998xt}.
\vspace{1cm}
\dots
\vspace{1cm}
The detector is illustrated in \FigureRef{fig:LHCbCrossSection}, showing
the overall scale of the experiment and the surrounding cavern structure.
\begin{sidewaysfigure}
%\begin{center}
\includegraphics[width=0.8\textheight]{lhcb-detector-cross-section}
\caption[Cross-section view of \LHCb, cut in the non-bending $y-z$ plane]%
{Cross-section view of \LHCb, cut in the non-bending $y-z$ plane.}
\label{fig:LHCbCrossSection}
%\end{center}
\end{sidewaysfigure}
The single-sided detector design was chosen in preference to a two-armed
design since the detector dimensions are restricted by the layout of the
IP8 (ex-Delphi) cavern in which \LHCb is located. Using all the available
space for a single-arm spectrometer more than compensates in performance
for the \about{50\percent} drop in luminosity.
\section{The \Cerenkov mechanism}
A Huygens construction in terms of spherical shells of probability for photon
emission as the particle progresses along its track shows an effective
``shock-front'' of \Cerenkov emission. This corresponds to an emission cone of
opening angle \thetaCerenkov around the momentum vector for each point on the
track,
%
\begin{subequations}
\label{eq:cosThetaCk}
\begin{equation}
\cos\,\thetaCerenkov &= \frac{1}{n \beta} +
\frac{\hbar k}{2p}%
\parenths{ 1 - \frac{1}{n^2} } \\
&\,\sim \frac{1}{n \beta}%
\label{eq:cosThetaCkApprox}
\end{equation}
\end{subequations}
%
where $\beta \equiv v/c$, the relativistic velocity fraction,
\section{Trigger system}
\label{sec:triggers}
An overview of the \LHCb trigger characteristics broken down by level
is shown in \Table~\ref{tab:TriggerDetails}:
\begin{table}
\begin{tabular}{lllll}
& L0 & L1 & HLT \\
\midrule
Input rate & \unit{40}{\MHz} & \unit{1}{\MHz} & \unit{40}{\kHz} \\
Output rate & \unit{1}{\MHz} & \unit{40}{\kHz} & \unit{2}{\kHz} \\
Location & On detector & Counting room & Counting room \\
\end{tabular}
\caption{Characteristics of the trigger levels and offline analysis.}
\label{tab:TriggerDetails}
\end{table}
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