The PHENIX Level-1 Trigger system

The PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) will study the dynamics of ultra-relativistic heavy ion collisions and search for exotic states of matter, most notably the Quark Gluon Plasma (QGP). Substantial event selectivity is needed at RHIC to enhance interesting events relative to more common ones and to satisfy the requirements of the data acquisition system. The first on-line screening is achieved by the Level-1 Trigger. The Level-1 Trigger is a beam-clock parallel-pipeline system that uses six Local Level-1 (LL1) algorithms pertaining to the six fastest PHENIX subdetectors, followed by a Global Level-1 (GL1) system that processes encoded LL1 reduced-bit data to issue up to 128 triggers. The LL1 algorithms operate on raw data to produce a first estimate of the number of electrons, photons, muons and hadrons as well as the transverse energy, event multiplicity, interaction time and vertex. The latency of the entire system is less than 40 beam crossings. The Level-1 Trigger is implemented using custom-designed 9U VME-P format boards.