A two level fastbus based trigger system for CDF

Abstract We describe a two level FASTBUS based trigger processor designed and built for the CDF detector at the Fermilab p p collider. The Level 1 decision is based on the global energy deposition in the calorimeters as well as on the presence of muon candidates and stiff tracks in the central drift chamber. The Level 1 decision is made in the 3.5 μs between beam crossings, incurring no deadtime while reducing a raw event rate of 50–75 kHz to a few kHz. The remaining events are passed on to Level 2. The Level 2 decision is driven by the topology of the event, operating on calorimeter clusters, central stiff tracks and muon candidates. Level 2 is designed to reduce the rate to 1–100 Hz, incurring less than 10% deadtime, before initiating readout of all the detector elements. A large fraction of the trigger hardware is used for both the Level 1 and Level 2 decisions.