Trigger and measurement system for small-angle scattering

A system for measurement and selection of small-angle scattering was developed for the study of high-energy muon interactions with nuclei. The trigger decision was obtained by using the information from more than 500 individual scintillation counters placed in and around the beam. They were distributed in 8 successive planes upstream and 4 planes downstream of the target. In the trigger logic, each beam particle in the 5 cm wide beam was identified and, a fast trigger signal was produced, only if the track was consistent with a scattering process. The beam rate was ∝107 s-1 and the decision time of the trigger processor, built in the Fastbus standard, was typically 80 ns. The reaction between 280 GeV muons and different target nuclei could be studied down to scattering angles of 1.6 mrad. The trigger rate with these conditions was of the order of 10-5 per incident beam particle. (orig.)