A sequential/parallel track selector

A medium speed (∼1 μs) hardware pre-analyzer for the selection of events detected in four planes of drift chambers in the magnetic field of the Omicron Spectrometer at the CERN SC is described. Specific geometrical criteria determine patterns of hits in the four planes of vertical wires that have to be recognized and that are stored as patterns of “1”s in random access memories. Pairs of good hits are found sequentially, then the RAMs are used as look-up tables.