Comparison of existing and proposed HEP data acquisition systems and their suitability for RHIC

In this note, a summary of these DACQ systems is presented for UA1, MARK II, D0, CDF, and SLD, focusing on the data acquisition stages and trigger rates. The suitability of these systems for a RHIC calorimeter detector with ports is then discussed. Although these DACQ systems have their individuality, they all use the common approach, of a multi-level trigger that reduces the rate and volume of the data to be recorded, in a number of appropriate steps. The first level trigger is analog, operates in the 1 μsec range, and has the purpose to reduce the interaction rate to a manageable rate of 105 hz or less. While a second level trigger is being formed, in a time range as short as 10 μsec for SSC detectors, the data can be compressed (zero suppression, pedestal subtraction, etc.) and is buffered. The second level trigger has usually some intelligence, in the form of programmable logic or micro-processors. The third level trigger is done by software. At this stage, it is current practice to employ a processor farm to assemble full events and implement the reconstruction necessary to perform the final event selection, prior to archival on tape or optical disc. The nature and amount of data processing performed at each level is flexible and depends on the application. The differences between the specific systems described below reside in: interaction rate and raw event size, type of primary data acquisition hardware and read-out scheme, choice of busses and processor farms. 6 references, 4 figure