Fnal E771 Fast Muon Trigger

A fast first level muon trigger, developed for and used in experiment E771 at Fermilab, for selecting events containing high energy muons, is described. The trigger finds events by matching the hits information received from three planes of resistive plate counters. The entire process, accomplished within 450 ns, reduces the total interaction rate by a factor of similar to 10(2) for the single muon trigger and a factor of similar to 10(4) for the dimuon trigger. The trigger logic is programmable, and it allows for an optimization of the signal to background ratio. The capability and performances of the trigger system are also described