Large Acceptance Measurement of Photons and Charged Particles in Heavy Ion Reactions

% WA98 \\ \\ The aim of the experiment is the high statistics study of photons and neutral hadrons, as well as of charged particles, and their correlations in Pb~-~Pb collisions. The photons are measured by: \begin{enumerate}[-] \item a 10~000 module LEADGLASS SPECTROMETER yielding high precision data on $ \pi ^0 $ and $ \eta $ at midrapidity (with transverse momenta 0.3 GeV/c $>$ p$ _{T} $ $>$ 4.5 GeV/c for $\pi ^0 $ and 1.5~GeV/c~$>$~p$ _{T}~$ $>$~4.0~GeV/c for $ \eta $ covering the $^{\prime\prime}$thermal$^{\prime\prime}$ as well as the $^{\prime\prime}$hard scattering$^{\prime\prime}$ regime beyond 3~GeV/c) and determination of the thermal and direct photon to $ \pi ^0 $ ratio. \item a pad preshower PHOTON MULTIPLICITY DETECTOR which, by comparing with the charged particle multiplicity measurement allows to determine the photon enrichment in an event or event class. \end{enumerate}\\ \\The charged particle setup contains:\\ \\\begin{enumerate}[-] \item a 4000 element SILICON PAD DETECTOR and a 4-inch SILICON DRIFT DETECTOR to measure the charged particle multiplicity. \item a MULTISTEP AVALANCHE TRACKING SYSTEM with optical readout for momentum measurement of negative tracks. \item a MULTISTEP AVALANCHE TRACKING SYSTEM with pad readout for momentum measurement of positive tracks. \item a TIME-OF-FLIGHT SYSTEM for each tracking system for particle identification. \end{enumerate} \\ \\This allows to correlate electromagnetic and charged hadronic data within event classes and to yield high statistics transverse momentum spectra of identified hadrons as well as Bose-Einstein correlation data.