A trigger processor for ARGUS

The ARGUS detector at the electron-positron storage ring DORIS consists of various particle detectors arranged in cylindrical symmetry in and around an axial magnetic field. A fast secondary trigger processor has been designed to find and count circular tracks in the r- phi -plane of the detector that originate from the interaction point. The processor serves as a filter in the trigger system of the ARGUS detector and is expected to reduce the rate of background triggers by two orders of magnitude. The processor hardware is built in ECL to perform simple operations with very high speed and partly in parallel. The track finding process takes about 9 mu s plus 3 mu s for each encountered track element. Control information is stored in memories that may be loaded via CAMAC from the online computer allowing easy adaption of the processor to different experimental conditions. (1 refs).