Operation, performance and upgrade of the CMS Resistive Plate Chamber system at LHC

The Resistive Plate Chambers are used in CMS as dedicated muon trigger detectors in both barrel and endcap regions. They also contribute to the identification, reconstruction and tracking of the muons, together with Drift Tubes in the barrel and Cathode Strip Chambers in the endcaps. In this paper a detailed report about the operation and performance of the system after three years of LHC activities with increasing instantaneous luminosity is given. This period allowed to accumulate enough statistics to measure the detector performance with an unprecedented accuracy on such a large amount of chambers. This provided new insights both on the detector fundamentals and on the related operational aspects. Special attention was devoted to the working point calibration procedures and to the stability of the system. A comparison between the initial and present performance is made, and an overview is given of what has been learned in almost three years of operation of one of the largest systems based on RPCs