The COMPASS trigger for Drell-Yan measurements

In 2014/15 the COMPASS experiment measured double-muon-production in the reaction of negative pions of 190 GeV/c with a polarised ammonia target. This process is called Drell-Yan process. The final state consists of two muons and a hadronic state. The hadrons and remaining beam pions were removed by an absorber directly behind the target, the remaining muon pairs were detected in the double stage COMPASS spectrometer. For a symmetric acceptance for positive and negative muons, the single muon trigger system had to be modified. The necessary modifications on the single muon trigger and the performance of the new trigger are presented.