The First-Level and High-Level Muon Triggers of the Compact Muon Solenoid Experiment at CERN

High transverse momentum muons are expected to play a crucial role in the discovery of the Standard Model Higgs, precision Standard Model measurements, as well as in the discovery of new physics such as Supersymmetry at CERN's new Large Hadron Collider. In order to provide efficient and precise muon detection, three muon systems are utilized in the Compact Muon Solenoid (CMS) experiment: Drift Tubes in the barrel, Cathode Strip Chambers in the endcaps and Resistive Plate Chambers throughout for trigger information complementary to the high-precision tracking measurements of the first two systems. The CMS trigger has to reduce the event rate from the LHC bunch-crossing rate of 40 MHz to a rate of approximately 100 Hz, the maximum that can be recorded for offline analysis. This enormous reduction is achieved in several subsequent levels: while the first level trigger reduces the initial rate to a maximum of 100 kHz employing fully pipelined custom-built electronics, the following higher trigger levels will run on a high-performance farm of commercial processors allowing for full flexibility. Muon-trigger algorithms employed at the first and higher trigger levels are discussed. Special emphasis is given to the First-Level Global Muon Trigger, which increases efficiency and considerably improves rate reduction by optimally combining trigger information of all three muon systems. Detailed Monte-Carlo simulations of expected trigger rates and trigger efficiencies are presented.