A 10 MHz Beam Counter and a Multiplicity Detector for the E864 Spectrometer

The E864 experiment at BNL requires a beam counter and multiplicity detector system that can perform at an incident beam rate of 10 Au ions per second. We have developed and tested a 150 m thick quartz Cherenkov beam counter and a scintillator based multiplicity-trigger counter during the rst run of this experiment in 1994. We obtained a time resolution of 78 ps for the beam counter at an incident beam rate 5 10 Hz and 100 ps at a rate of 1 10 Hz. Pulse height discrimination is used to obtain a minimum bias and a 10% centrality trigger from the multiplicity detectors. The multiplicity counter has a time resolution of 250 ps.