Integration, Installation, and Commissioning of Large Monitored Drift Tube Chambers of the ATLAS Barrel Muon Spectrometer

The ATLAS experiment at the Large Hadron Collider (LHC) at CERN is currently being assembled to be ready to take data in 2007. Its muon spectrometer is designed to achieve a momentum resolution of better than 10% at 1 TeV. The barrel part of the muon spectrometer consists of a toroidal air-core magnet which is instrumented with three layers of monitored drift tube (MDT) chambers as precision tracking detectors. The installation of the muon detectors has started in January 2005. The Max-Planck-Institut fur Physik and the Ludwig-Maximilians-University in Munich have built 88 MDT chambers for the outermost barrel region, each covering an area of 8 m². To ensure their proper operation in the experiment, the MDT chambers have to pass a set of stringent tests both at the production site and after their delivery to CERN; at CERN, the MDT chambers are also integrated with resistive plate chambers (RPCs) of the trigger system to form muon stations. After their installation in the detector, the muon stations are further tested and commissioned with cosmic rays. We report on our experience with the chamber tests, the integration procedure and installation of the muon stations in the experiment. First results of their commissioning in the ATLAS detector will be presented, as well as results of the MDT chamber calibration and alignment studies performed with cosmic rays with and without magnetic field.