THE ZEUS 1ST LEVEL TRACKING TRIGGER

The ZEUS experiment has a three-level trigger system to select electron-proton interaction events from a large anticipated background of proton beam-gas. The first level decision is formed using pipelined hardware processors clocked at the 96 ns beam crossing frequency. A vital component of this decision is discrimination against upstream events using tracking detector information. The processors use three-dimensional space points measured in the central tracking detector to find pointing tracks over most of the theta range, and include forward tracking detector information to improve the resolution and angular coverage in the proton forward direction. The processor design status and performance simulation results are presented.