Architecture and performance of the DELPHI trigger system

The authors describe in detail the basic concepts of the design, the composition of the data flow, and the tools developed to monitor the trigger in real time. The results of the trigger performance in terms of efficiencies achieved during the first two and a half years of operation in the LEP (Large Electron Positron Collider) machine are also shown. So far, a total of ~10⁶ hadronic Z⁰s have been collected from 21 million recorded events. The DELPHI trigger system provides an efficiency nearly 100% over the covered solid angle for all particles and physical channels. The system has also proved to be stable despite very different beam conditions. This is a consequence of the high redundancy provided by the different detectors for all e ⁺e^- final state processes, which also ensures a method for calculating the absolute trigger efficiencies using data only