COMPASS COmmon Muon and Proton Apparatus for Structure and Spectroscopy

%NA58 %title\\ \\COMPASS is a new fixed target experiment at the SPS to study hadron spectroscopy with hadron beams (up to 300~GeV/c) and hadron structure with polarized muon beams (100-200~GeV/c).\\ \\The main physics objective of the muon beam program is the measurement of $\Delta$G, the gluon polarization in a longitudinally polarized nucleon. More generally, it is planned to measure the flavour separated spin structure functions of the nucleons in polarized muon - polarized nucleon deep inelastic scattering, both with longitudinal and transverse target polarization modes. For these measurements a new 1.3~m long polarized target and a superconducting solenoid with 200~mrad acceptance will be used.\\ \\The hadronic program comprises a search for glueballs in the high mass region (above 2~GeV/c$^{2}$) in exclusive diffractive pp scattering, a study of leptonic and semileptonic decays of charmed hadrons with high statistics and precision, and Primakoff scattering with various probes. A detailed investigation of charmed and doubly charmed baryons will be performed in a second stage of the experiment. For these measurements a highly segmented silicon target detector and high resolution electromagnetic calorimeters will be constructed.\\ \\The setup consists of two independent spectrometers, one for small angle and one for large angle particles, giving a large angular acceptance for all measurements. Each spectrometer comprises full particle identification using RICH detectors, electromagnetic and hadronic calorimetry and muon detection. Owing to precision tracking with silicon detectors, gaseous strip detectors and drift tubes high momentum resolution is obtained.\\ \\The measurements will be performed with high intensity beams (2 10$^{8}$ muons/spill and 10$^{8}$ hadrons/spill) allowing to collect the needed statistics. The fully pipelined readout scheme can cope with the foreseen trigger rates (about 100~Khz) without noticeable deadtime.\\ \\Data taking will start in the year 2000 with the muon programme.\\ \