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 10^7 Au ions per second. We have developed and tested a 150 micrometer thick quartz Cherenkov beam counter and a scintillator based multiplicity-trigger counter during the first run of this experiment in 1994. We obtained a time resolution of 78 ps for the beam counter at an incident beam rate 5 x 10^5 Hz and 100 ps at a rate of 1 x 10^7 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.