The Muon Spectrometer of the ATLAS experiment is a large and complex system relying on several detector technologies. The simulation and reconstruction of muon events require a very careful description of these detectors, some of which provide a muon trigger while the others make precision measurements of tracks. A precise description of the passive materials, toroidal magnet systems and shield is also needed to account for Coulomb scattering and energy losses. Finally, the spectrometer performance is enhanced by the alignment of its precision chambers, so the detector description model must fully implement misalignments and deformations. We present the Detector Description chain employed in the Muon system and its integration in the ATLAS software framework. It relies on a database technology and a standard set of geometrical primitives common to all ATLAS subsystems. The Muon Detector Description has been used successfully in the context of the ATLAS Data Challenges, where it provides a unique and coherent geometry source for the simulation and reconstruction algorithms. It has also been validated in the context of the experimental program of the ATLAS testbeams, where analyses of the treatment of chamber alignment in track reconstruction relies crucially upon the detector description model.
Commissioning of the muon track reconstruction in the ATLAS experiment