Abstract
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 m2. 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 the scope of muon triggering and detection. The measurements presented here allow to plan a strategy for the data taking in the next years and make some predictions about the detector performance at higher luminosities. They also improve the knowledge on RPC detector physics.
Highlights
Resistive Plate Chambers provide the barrel region of the ATLAS detector with an independent muon trigger and a two-coordinate measurement
An ATLAS RPC is made of two layers, each with two 2 mm thick bakelite laminate plates and provides 2 η and 2 φ strip planes
The high voltage (HV) working point is chosen to be at 9.6 kV at a temperature of 24◦C and a pressure of 970 mbar
Summary
Resistive Plate Chambers provide the barrel region of the ATLAS detector with an independent muon trigger and a two-coordinate measurement. 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 behaviour 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. The ability to control by tuning thresholds, and monitoring the current of each RPC gap has shown to be very powerful for the detector operation both for tracing problems and fine tune the detector This is important as the RPC performance and aging is strongly related to the environmental parameters, namely the temperature (T ), the atmospheric pressure (P), and the relative humidity
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