The trigger system for the COMPASS electromagnetic calorimeter ECAL1

Since 2006 the set-up of the COMPASS experiment at CERN includes a second electromagnetic calorimeter, the ECAL1, placed in the first spectrometer stage. It consists of lead glass modules of three different sizes used from previous experiments. A new trigger system is being developed making use of the ECAL1 information. For this purpose the photomultiplier signals are split into two, one signal is used for the sampling ADC and the second is used as input to a summation stage. Here analog sums of 4 x 4 modules are build. The trigger logic requires at least one summed signal above a certain threshold. Some results of the 2006 data taking will be presented. (orig.)