The Level-2 muon trigger at D0

The upgraded DO detector at the Fermilab Tevatron will feature a new three-level trigger based on physics object recognition. The Level-2 muon trigger is required to use the timing data from the muon wire chambers and scintillator to rind track segments and then match those segments with Level-1 muon and fiber tracker trigger information. To accomplish this task, the Level-2 muon trigger features a three-stage approach. The first stage uses a parallel set of custom VME cards that route data through a high-speed and configurable bus to a series of 200-MHz Texas Instruments digital signal processors. This will reduce the large data volume distributed over some 140 sources to a manageable set of three-dimensional track stubs from the 16 cards. Data from these boards are combined to form muon track candidates in the second stage using another custom board built around a 500-MHz Compaq Alpha processor chip. In the third stage, another Alpha-based board matches the muon tracks with tracks found in the central tracking trigger and is able to correlate those muons with other physics objects in the event, such as jets. Queueing simulations of the system running at a rate consistent with the expected input rate and desired background rejection have shown that the Level-2 muon trigger will produce a dead time less than 5%.