The Crystal Barrel: Meson Spectroscopy at LEAR with a 4$\pi$ Detector

% PS197 \\ \\The Crystal Barrel is a 4$\pi$ spectrometer designed to provide complete and precise information on practically every final state produced in $\bar{p} p $ and $\bar{p}d $ annihilations at low energy and to collect high statistics data samples. Selective triggers can be applied when necessary. \\ \\The physics goal is to identify all light mesons in the mass range from 0.14 to 2.3~GeV/c$^{2}$, to determine their quantum numbers and decay properties and to study the annihilation dynamics. The main interest is to find the glueball and hybrid degrees of freedom predicted in the framework of Quantum Chromodynamics. \\ \\\noindent The principal components of the apparatus are: \begin{enumerate}[1.] \item A barrel shaped electromagnetic calorimeter for the detection of photons. It consists of 1380~CsI(Tl) crystals read out by photodiodes via wavelength shifter. \item A 22-layer cylindrical jet drift chamber for the tracking of charged particles. It contains 585 sense wires read out at both ends. Charge division provides information on the coordinate parallel to the wires and the total charge deposit is used to measure dE/dx. \\ \\\item A silicon $\mu$-strip vertex dectector to provide a multiplicity trigger very close to the target and to improve the momentum and vertex resolution. It is subdivided into 15~modules, each with 128 strips and surrounds the target at a radius of 1.2~cm. \\ \\\item The incoming cooled antiprotons (beam momenta from 0.1 to 1.9~GeV/c) are detected by silicon hodoscopes. The whole detector is embedded in a solenoidal magnet with field strength up to 1.5~T.