A PIPELINED FIRST-LEVEL TRIGGER FOR THE H1 FORWARD-MUON SPECTROMETER

We have built a fast, pipelined first-level trigger processor for the H1 experiment at HERA. The trigger finds tracks in the forward-muon spectrometer which point back to the interaction vertex. The inputs to the trigger come from drift chambers with a 6 cm drift space corresponding to a maximum drift time of 1.2 mu s. These chambers consist of two layers of drift cells whose staggered configuration makes it possible to extract the time at which a particle traversed the chambers to better than one HERA bunch-crossing period, 96 ns. The trigger hardware exploits this characteristic in a real-time operation, and is able to find pointing tracks and associate them to production in a specific electron-proton crossing. The trigger processor must be deadtime free. It operates in a pipelined mode with 48 ns steps and has a latency of about 22 HERA bunch-crossing periods. The compact design is based on two semi-custom integrated circuits. Both are field-programmable 32 X 32 coincidence matrices, one having serial loading of its inputs and the other using parallel loading. The system was installed in the H1 experiment early in 1993 and has run successfully since then.