The ALICE muon trigger system: Cosmic ray commissioning and first beam-induced events

The ALICE experiment is designed to study strongly interacting nuclear matter which will be produced in heavy ion collisions at the Large Hadron Collider (LHC). The muon spectrometer of the ALICE experiment is equipped with a trigger system based on resistive plate chambers. A commissioning phase was started in 2008 with the detection of cosmic rays and induced particles of the first beam injections into the LHC ring. The performances of the whole muon trigger system achieved during the commissioning phase are presented.