Implementation and performance of the optical fiducial volume trigger used with the rapid cycling bubble chamber

Abstract A description is given of the software algorithms used for the Optical Fiducial Volume Trigger system (OFVT) and the implementation on-line. The OFVT system has the purpose of enhancing the efficiency of the trigger system for the Rapid Cycling Bubble Chamber (RCBC) of the European Hybrid Spectrometer (EHS). One obtains an efficiency for good events of 80–90% and a rejection efficiency for events outside the bubble chamber fiducial volume of 60–70%. With the use of OFVT the fraction of pictures containing a useful event rises from 30% to 55%.