The ZEUS first and second level trigger

The ZEUS trigger has a three-level structure. At the first level, data are processed in a pipelined manner, while the readout data are kept in analog or digital pipelines. At the second-level, arrays of microprocessors analyze the digitized data to reduce the trigger rate by a factor of 10 from 1 kHz to 100 Hz. After the event has been assembled by the event builder, it is analyzed by a processor station, part of a farm of 36 stations, providing an event reduction of by factor of 10-20. The maximum rate of events (a mixture of background, almost real photoproduction, and deep-inelastic scattering events) that can be written to tape at the DESY-IBM after the selection in the three-level trigger system is 5-10 Hz at an average event size of about 100 Kbyte.<
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