The "neutral" trigger system for the selection of K-o --> 2 pi(o) --> 4 gam
ma decays of the NA48 CP-violation experiment is described. The trigger sys
tem has been implemented in a 40 MHz "dead-time free" pipeline to allow lar
ge rate reduction and high-trigger efficiency. The trigger decision is base
d on the information from 13340 cells of the electro-magnetic calorimeter.
Every 25 ns the energy, the centre of gravity, the kaon lifetime and the nu
mber of peaks in calorimeter projections are calculated in the trigger. The
pipeline system is described and the performance of the trigger during the
1997 data-taking period is discussed. (C) 1998 Published by Elsevier Scien
ce B.V. All rights reserved.