The ZEUS calorimeter trigger

Summary form only given, as follows. The calorimeter trigger for the ZEUS detectors at the HERAe-p collider is designed to collect charged and neutral current, photoproduction, and exotic physics events while reducing beam gas background using three different approaches. They are: (1) detection of isolated electrons and muons using pattern analysis logic, (ii) identification of patterns of energy deposits obtained from local energy sums, and (iii) recognition of characteristic deposits of total transverse and missing transverse energy. This is done by calculating energy sums, searching for energy clusters, isolated muons, and electrons, and summarizing regional information for correlation with other detector elements. The trigger completes these tasks in a pipelined fashion in 2 microsec, accepting new data and shipping out results once ever 95 nsec. It uses digital logic with memory lookup tablesto provide programmable flexibility for changing calibration, thresholds, and the types of tests made. >