PHENIX trigger system

A two level trigger system has been implemented in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). Level 1 trigger system (LVL1) processes the reduced data from a part of the detector subsystems in parallel and makes a decision on each beam crossing. For each accepted event the information from LVL1 is added to the detector data stream. A detector partitioning mechanism accomplished in LVL1 permits to operate PHENIX both as a whole detector (single partition) as well as a group of different combinations of the detector subsystems (multiple partitions). The Level 2 trigger system (LVL2) makes a fast analysis of each accepted event and decides if its data have to be stored or to be discarded. A description of the components and operation of the PHENIX trigger system is presented in this article.