A digital trigger for the electromagnetic calorimeter at the COMPASS experiment

At the COMPASS experiment at CERN's SPS many physics channels containing neutral particles are studied. These particles are identified by two electromagnetic calorimeters covering different regions of transverse momentum. For certain physics the main signature is described by these neutral particles requiring a calorimetric trigger system. The method described here is based on the existing front end electronics and uses digital pulse shape analysis techniques. With this approach a flexible trigger system was implemented. Because no new hardware had to be produced, the development costs were minimized. The implementation of the trigger as well as the performance, measured during the 2009 run will be discussed.