The DISTO first level trigger at SATURNE

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multi-particle final states produced in pp scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the p/spl I.oarr/p/spl rarr/pK/sup +/Y/spl I.oarr/ (Y=/spl Lambda/, /spl Sigma//sup 0/ or Y*) reaction and vector meson production (/spl phi/, /spl omega/, and /spl rho/) in pp collisions. The common signature of such events is the multiplicity of four charged particles in the final state. A flexible 1st level trigger which uses topological information from fast detectors (scintillating fibers and hodoscope) has been built. It is completely software programmable through a menu-driven user interface and allows switching between production and monitor triggers on successive beam spills.