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{\huge The Crystal Barrel}\\[0.25cm]{\LARGE An Experiment at LEAR
and ELSA}\\[1cm]{\large A seminar talk given in the
lecture}\\[0.25cm]{\Large "Experimental Methods in Elementary
Particle Physics"}\\[1cm]{\large{by Eric Gutz {\normalsize
(CB-ELSA)}}\\[0.5cm]\large June $16^{th}$ 1999}
\\ [2cm]\includegraphics[width=9cm,height=10.5cm]{BARREL2.bmp}\\
\newpage

{\huge \bfseries The Electromagnetic Calorimeter 1}\\[1.5cm]
\includegraphics[width=10cm,height=10cm]{open_barrel.bmp}\\[2cm]
\begin{tabular}{ccc}\hline
 & & \\General layout & Barrel configuration\\ Polar angle range
[deg] & 12--168\\ Solid angle & approx. 98\% of 4$\pi$\\ Free
inner length [mm] & 540\\ Free inner radius [mm] & 270\\ Number of
elements & 1380\\ Scintillator & CsI(Tl)\\ Active length [mm] &
300 (16.1 $L_R$)\\Readout & WLS and photodiode\\ Total mass [kg] &
$3.8\cdot 10^3$\\ & \\ \hline
\end{tabular}
\newpage

{\huge \bfseries The Electromagnetic Calorimeter 2}\\[1.5cm]
\includegraphics[width=18cm,height=10cm]{calfs.bmp}\\[1cm]
{\large Resolutions:}\\[0.25cm]
\begin{tabular}{ccc}\hline
 & & \\Energy ($933.4 MeV$) & $\sigma_E=23.3 MeV (2.5\%)$
\\
Energy ($95 MeV$) & $\sigma_E=4.8 MeV (5\%)$\\ angular ($E>50MeV$)
& $\sigma_{\Theta}<1.5^o$\\ & \\ \hline
\end{tabular}\footnote{corresponding to $\frac{1}{^4\sqrt{E}}$-dependence}
\newpage

{\Large \bfseries The CsI(Tl) - Modules 1}\\[2cm]
\includegraphics[width=18cm,height=8cm]{module.bmp}\\(1)
0.1 mm titanium can, (2) printed circuit board, (3) filters for
bias and power supplies, (4) preamplifier, (5) light fibre, (6)
brass cover, (7) wavelength shifter (WLS), (8) photodiode\\[2.5cm]
\begin{tabular}{ccc}\hline
 & \\Density [g/cm$^3$] & 2.53\\ Radiation length $L_R$ [cm] & 1.86\\
Light output & 0.85 relative to NaI\\ Maximum emission & at 550
nm\\ Decay time [$\mu$s] & 0.9\\ Photon yield /MeV &
$4.5\cdot10^4$\\ & \\ \hline
\end{tabular}
\newpage

{\Large \bfseries The CsI(Tl) - Modules 2}\\[1cm]
\includegraphics[width=18cm,height=7.1cm]{module_ph.bmp}\\[1.5cm]
\includegraphics[width=11.3cm,height=8.1cm]{mod_plot.bmp}\\[0.5cm]
Optical matching of CsI(Tl) scintillator to the WLS. Dashed curve:
spectral emission of CsI. Full line: measured transmission of WLS.
Dotted line: measured spectral emission of WLS.
\newpage

{\Large \bfseries The CRYSTAL BARREL at LEAR}\\[1cm]
\includegraphics[width=9.4cm,height=11cm]{cern.bmp}\\[1cm]
\includegraphics[width=9cm,height=6cm]{cbcern.bmp}
\newpage

{\huge \bfseries The Detector Array}\\[2.5cm]
\includegraphics[width=18cm,height=10.4cm]{detcern.bmp}\\[1cm]
{\Large(1) magnet yoke, (2) magnet coils, (3) CsI barrel, (4) jet
drift chamber, (5) proportional chamber, (6) liquid hydrogen
target, (7) endplate (one half)}
\newpage

{\huge \bfseries Jet Drift Chamber}\\[1.5cm]
\includegraphics[width=18cm,height=11.1cm]{jdc.bmp}\\[1.5cm]
\begin{itemize}
\item 30 azimuthal sectors, 23 radial layers, spacing $8mm$
\item inner radius $63mm$, outer radius $239mm$ (sense wires),
sensitive length $399mm$ $\rightarrow$ solid angle equal to $95\%$
of $4\pi$
\item 2430 aluminium wires ($152\mu m$ diameter), $0.64\mu m$ gold
coating
\item gas: 90:10 mixture of CO$_2$/isobuthane (C$_4$H$_{10}$)
\item voltage sense wires (grounded) - sector midplane: $-2318V$
\end{itemize}
\newpage

{\Huge \bfseries CB-Physics at LEAR}\\[1.5cm]{\large
\includegraphics[width=14cm,height=9.3cm]{lear2.bmp}\\[1cm]
\begin{itemize}
\item $\bar{p}p$ - fixed target experiments (liquid and gaseous H-targets)
\item study of produced mesons and their decay products
\item identification of predicted and new mesons (''exotic mesons``)
\item identification of glueball at $1500MeV$
\end{itemize}}
\newpage

\includegraphics[width=18cm,height=21cm]{4events.bmp}\\
\newpage

{\Huge \bfseries The CRYSTAL BARREL at ELSA}\\[1.5cm]
\includegraphics[width=16cm,height=8.8cm]{elsaplan_2.bmp}\\[0.5cm]
\includegraphics[width=16cm,height=9.2cm]{cbarea.bmp}\\
\newpage

{\Huge \bfseries The Tagging System}\\[2cm]
\includegraphics[width=18cm,height=8cm]{tagger.bmp}\\[1.5cm]
\begin{tabular}{ccc}\hline
 & \\ Scintillators & 14\\ Wires MWPC 1 & 208\\ Wires MWPC 2 &
 144\\ Overlap MWPCs & 206-211\ & \\ Energy-channels & 349\\ Energy
 range MWPC 1 & 94.4\%-79.5\%\\ Energy
 range MWPC 2 & 80.8\%-31.0\%\\ & \\\hline
\end{tabular}\\[0.5cm]
Specifications TOPAS2 tagger
\newpage

{\huge \bfseries The Detector Array}\\[2cm]
\includegraphics[width=18cm,height=6.3cm]{elsa_array.bmp}\\[1cm]
\includegraphics[width=18cm,height=8.8cm]{gesamt.bmp}\\
\newpage

{\huge \bfseries The Inner Detector}\\[2cm]
\includegraphics[width=10cm,height=8.3cm]{id.bmp}\\[1.5cm]
\includegraphics[width=11.4cm,height=4.3cm]{id_plot.bmp}\\[0.5cm]
Invariant mass-spectra without (left) and with (right) the inner\\
detector (based on Monte-Carlo-simulations)
\newpage

{\Large \bfseries The Magnetic Spectrometer}\\[1cm]
\includegraphics[width=8cm,height=8.9cm]{spektro.bmp}\\[1cm]
{\Large \bfseries The TOF Spectrometer}\\[1cm]
\includegraphics[width=8cm,height=7.5cm]{tof.bmp}\\
\newpage

{\Large \bfseries The TAPS Detector}\\[1cm]
\includegraphics[width=12.2cm,height=8cm]{taps1.bmp}\\[1cm]
{\Large \bfseries The Lead-Glass Wall}\\[1cm]
\includegraphics[width=9.6cm,height=8cm]{lgw.bmp}\\
\newpage

{\Huge \bfseries CB-Physics at ELSA}\\[1.5cm] {\LARGE \bfseries
Photoproduction of baryon resonances}
\\[1cm]
{\Large \bfseries Search for missing
resonances}\\[1cm]\end{center}{\large \bfseries
\begin{itemize}
\item 3-quark model of baryons $\rightarrow$ certain number of
resonances (internal degrees of freedom)
\item Large number of predicted resonances not (yet) observed
\item Solutions:
\begin{enumerate}
\item \textsc{Lichtenberg}: Wrong model, baryons $\rightarrow$
quark - diquark system
\item Missing resonances do not couple to $\pi$N (nearly all existing data results from $\pi$N scattering)
\end{enumerate}
\item Missing resonances should couple to final states such as
e.g. $\Delta\pi$, N$\eta$, N$\rho$, N$\omega$ and N$\eta'$
($\eta$-, $\eta'$- and $\omega$-channels investigated by CB)
\end{itemize}
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