Search

The Muon Spectrometer for the ATLAS experiment at the LHC is designed to identify muons with transverse momentum greater than 3 GeV/c and measure muon momenta with high precision up to the highest momenta expected at the LHC. The 50-micron sagitta resolution translates into a transverse momentum resolution of 10% for muon transverse momenta of 1 TeV/c. The design resolution requires an accurate control of the positions of the muon detectors and of the distortions of the nominal layout of individual chambers, induced by mechanical stress and thermal gradients during the experiment operation. Accurate calibration of the time to distance relation in the Monitored Drift Tubes is also required to reach design performance. We describe the software chain that implements corrections for the alignment and calibration of the chambers, as well as the algorithms implemented to perform pattern recognition and track fitting in the ATLAS Muon Spectrometer. In particular, we report on the performance of the complete software chain in the context of first single-beam LHC running as well as ATLAS combined cosmics data taking.

The size and complexity of LHC experiments raise unprecedented challenges not only in terms of detector design, construction and operation, but also in terms of software models and data persistency. One of the more challenging tasks is the calibration of the 375000 Monitored Drift Tubes, that will be used as precision tracking detectors in the Muon Spectrometer of the ATLAS experiment. An accurate knowledge of the space-time relation is needed to reach the design average resolution of 80 microns. The MDT calibration software has been designed to extract the space-time relation from the data themselves, through the so-called auto-calibration procedure, to store and retrieve the relevant information from the conditions database, and to properly apply it to calibrate the hits to be used by the reconstruction algorithms, taking into account corrections for known effects like temperature and magnetic field. We review the design of the MDT calibration software for ATLAS and present performance results obtained with detailed GEANT4-based simulation and real data from the recent combined test beam. We discuss the implementation of the conditions database for MDT calibration data in the framework proposed by the LHC Computing Grid (LCG). Finally, we present early results from detector commissioning with cosmic ray events and plans for the ATLAS Computing System Commissioning test in 2006.