The CHAOS second level trigger. A fast, programmable ECL trigger for a magnetic spectrometer using multiwire proportional chambers

A versatile second level trigger has been developed for the CHAOS facility at TRIUMF using fast ECLine trigger modules augmented by some specially constructed modules. It consists of a primary stage and two optional secondary stages. The primary track finding stage is capable of making a decision based on track vertex, polarity and momentum. The next stage is able to reject events based on the correlation between track momentum and scattering angle. The third stage can make a cut on the sum of the momenta of two tracks. In addition there is an extra parallel stage that is responsible for ensuring that the beam particle has the correct incoming trajectory. All stages are programmable and, depending on experimental conditions and trigger configuration, usual rejection times are between 2 and 4 μs.