The RPC system for the CMS experiment

The CMS experiment at the CERN Large Hadron Collider (LHC) is equipped with a redundant muon trigger system based on drift tubes chambers (DT) and cathode strip chamber (CSC), for the precise position measurement, and resistive plate chambers (RPC), for the bunch crossing identification and a preliminary fast measurement of the muon transverse momentum. The CMS RPC system is constituted by 480 chambers in the barrel and 756 chambers in the forward corresponding to a total surface of about 3500 m2. The design and construction has involved many laboratories scattered all over the word. An accurate quality control procedure has been established at different levels of the production to achieve final detectors with operation parameters well inside the CMS specifications. In the summer 2006 a preliminary slice test involving a fraction of the CMS detector was performed. The performance of the RPC system with cosmic rays was studied versus the magnetic field using final running hardware and software protocols. Results on the RPC main working parameters are reported.