Study of the RPC Level 1 Trigger efficiency of the Compact Muon Solenoid at LHC with cosmic ray data

We report on a study of the Resistive Plate Chambers (RPC) Level 1 Trigger system efficiency in the Barrel of the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider. The method used to study the efficiency exploits the independence of the CMS Drift Tube and RPC trigger systems. Muon tracks in the event are triggered and reconstructed using the Drift Tube subsystem only, and for each of them we search for a compatible RPC L1 trigger object. We discuss in detail the results obtained with cosmic ray data taken in 2008-2009.