THE DISTO FIRST LEVEL TRIGGER AT SATURNE

The DISTO collaboration has built a large-acceptance magnetic spectrom eter designed to provide broad kinematic coverage of multi-particle fi nal states produced in pi, scattering. The spectrometer has been insta lled in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the (p) over right arrow p --> p K(+)(Y) over right arrow (Y = Lambda, Sigma(0) or Y) reaction and vec tor meson production (phi,omega and rho) in pp collisions. The common signature of such events is the multiplicity of four charged particles in the final state. A flexible Ist level trigger which uses topologic al information from fast detectors (scintillating fibers and hodoscope ) has been built. It is completely software programmable through a men u-driven user interface and allows switching between production and mo nitor triggers on successive beam spills.