Programmable trigger for electron pairs in ring image Cherenkov counters

A programmable trigger processor for the recognition of Cerenkov rings in a RICH (ring image Cerenkov) counter is described. It identifies open electron pairs and suppresses close conversion and Dalitz pairs within 20 μs. More generally, the system can be used for correlating pixel images with pattern masks in order to locate all relatively well defined patterns of a certain type. The trigger processor consists of a systolic processor array of 160×176, i.e. 28160 identical processing elements (PEs) that filter out open electron pairs, and a pseudo adder array that determines whether there was at least one such pair. Ring identification is done by a two-dimensional correlation of the input image with a circle, yielding the probability of finding circles at certain locations. All PEs run synchronously at a clock frequency of 30 MHz. The total computing power therefore amounts to 844800 million operations/s, where a typical operation is the combination of a 6-b addition and a shift