Performance, Operation and Detector Studies with the ATLAS Resistive Plate Chambers

Resistive Plate Chambers provide the barrel region of the ATLAS detector with an independent muon trigger and a two-coordinate measurement. The chambers, arranged in three concentric double layers, are operated in a strong magnetic toroidal field and cover a surface area of about $4000, m^2$. During 2011 the LHC has provided proton-proton collisions at 7 TeV in the center-of-mass frame with a steady increase in instantaneous luminosity, summing up to about 5 $fb,^{-1}$. The operational experience for this running period is presented along with studies of the detector performance as a function of luminosity, environmental conditions and working point settings. Non-event based information including in particular the large number of gas-gap currents, individually monitored with nA accuracy, have been used to study the detector behavior with growing luminosity and beam currents. These data are shown to provide, when calibrated, an independent luminosity measurement and a crucial handle for understanding the ATLAS backgrounds well beyond of the scope of Muon triggering and detection. Running such a large RPC system at a luminosity lower than nominal represents a unique opportunity to accumulate knowledge on the detector physics, far beyond the past ageing and performance studies which were limited by the modest numbers of detectors under test. This run allowed to gain experience on the detector operation and helped to plan a strategy for the data taking in the next years and the direction to take for the system upgrade in view of the future high luminosity runs at the LHC.}