Study of the RPC Level-1 trigger efficiency in the compact muon solenoid at LHC with cosmic ray data

We report a study of the Resistive Plate Chambers (RPC) Level-1 (L1) trigger system efficiency in the Barrel of the Compact Muon Solenoid (CMS) detector of LHC in the same region covered also by the DT trigger system. The method used to study the efficiency exploits the independency of the CMS Drift Tube (DT) 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 method and the results of the performance obtained with cosmic ray data taken in 2008-2009.