Design and performance of the fermilab E781 (SELEX) hardware scattering trigger

The design and performance of the Fermilab E781 (SELEX) Hardware Scattering Trigger (HST) are described. This trigger functioned by distinguishing beam scattering at small angles ( > 150 mu rad) from non-interacting beam. Six 50 mu m pitch silicon planes grouped in three (x,y) stations, two before and one after the target, were used as the particle detectors. The triggering system involved 1920 channels of readout providing data to the Fast Encoding and Readout System (FERS) with programmable trigger logic processor. The overall system was tested successfully at Fermilab during the 1996-1997 fixed target run. The encoding time of the readout part of the FERS device was 30 ns and the processor decision time was 55 ns. The HST provided an output signal 250 ns after beam traversal of the target. (C) 1999 Elsevier Science B.V. All rights reserved.