Multiple time digitizers and a trigger system for drift chambers

The architecture of a readout system is described which will be used in conjunction with the muon detector in the UA-1 experiment at the pp collider at CERN. In addition to measuring drift time for spatial information, the system provides a fast trigger (<1 mu s after drift time) and a second level trigger decision based on a fast microprocessor. The fast trigger part allows the use of the muon detector as an active trigger element, while a second level trigger decision using the detailed digitizer data is included for adequate reduction of the trigger rate. The multiple time digitizer (MTD) is based on the use of fast RAMs (256*4) as 125 MHz shift registers, giving time bins of 8 ns and a time range of 2 mu s (256*8 ns). The high input rate has imposed a fast readout and transfer to a buffer in the controller. The data in this buffer is reordered according to wire number and corresponding times. Together with look-up tables this allows fast processing of the data for a second level trigger. (9 refs).