The trigger system of the NOMAD experiment

The NOMAD trigger system is described in the present paper. It is made up o f a large area plastic scintillator veto system, two trigger scintillator p lanes inside a 0.4 T magnetic field and their associated trigger electronic s. Special features of the system consist of the use of proximity mesh phot omultipliers which allow the trigger scintillators to operate in the magnet ic field, and the use of custom-built VME modules which perform the trigger logic decisions, the signal synchronisation and gate generation, event cou nting and livetime calculations. This paper also includes a description of each of the NOMAD triggers, with their calculated and measured rates, effic iencies and livetimes. (C) 1999 Elsevier Science B.V. All rights reserved.