Muon trigger system in the TOPAZ detector

A redundant muon trigger system was implemented at the TOPAZ detector for the phase-II TRISTAN experiment. This system is mainly based on fast signals from barrel muon chambers, and is free from the other tracking detectors. The trigger rate has been stable at 0.5 Hz, which was dominated by cosmic-ray background. The trigger efficiency was obtained to be 92.5±0.7% for the e−e+ → μ+μ−(γ) process in the polar-angular region of |cosθ μ|<0.63. With this system, the inefficiency of the previous trigger system was measured with an accuracy of O(0.1%) for the above process.