Optimization and Calibration of the Drift-Tube Chambers for the ATLAS Muon Spectrometer

The final phase of preparations for the ATLAS experiment at the future Large Hadron Collider (LHC) has begun. In the last decade the collaboration has carried out various test-beam experiments to study and optimize prototypes of all subdetectors under more and more realistic conditions. To enhance the detector-physical understanding, these hardware activities were complemented by detailed simulations. In parallel the development of reconstruction software has made important progress. The present work focusses on some advanced aspects of optimizing the Monitored Drift Tube Chambers (MDT) for operation as precision chambers in the Muon Spectrometer. It will be shown how this system has been tuned for maximum performance in order to meet the ambitious goals defined by the objectives of LHC particle physics. After defining the basic detector parameters, the tubes' capability of running in ATLAS's high-rate gamma radiation background was verified. Both tasks necessitated several years of gathering experience in muon test beams to which the author has contributed together with colleagues from institutes spread over the entire globe. Although efforts have been made to concentrate on issues for which the writer bore the full responsibility, it was sometimes unavoidable -- in view of a more coherent treatment of sophisticated contexts -- to also display results contributed by other collaborators. This is particularly true for the analysis of the high-rate behaviour of drift tubes which was shared with M. Aleksa (CERN), N. Hessey (LMU, now NIKHEF) and W. Riegler (Harvard, now CERN). The employment of a silicon microstrip tracker in the test-beam experiments yielded an unprecedented precision in the understanding of the subtleties of drift-chamber physics. Chapter 6 presents an approach for taking advantage of this knowledge in the reconstruction of muon tracks through a multilayer of tubes. The momentum resolution and the track reconstruction efficiency of the muon spectrometer achieved with the optimized detector system were investigated in a Monte Carlo simulation. A central aspect of this study was the impact of the non-Gaussian errors in the drift-tube response near the anode wires on the spectrometer performance. Finally, techniques for the calibration of the space-time relationship of drift tubes were developed. Since in ATLAS no external reference detector will be available, the muon system has to be self-calibrating. This task will be accomplished by exploiting muon tracks from normal LHC operation. For each calibration method the attainable precision and the applicability for ATLAS MDT chambers are discussed. Here again, the results from the beam tests proved to be an indispensable input. Based on these insights a scenario for the in-situ calibration of all ATLAS MDT chambers is outlined. This includes a strategy for the definition of the spatial ``autocalibration zones'' in the spectrometer within which a calibration of the space-time relationship is valid. A simple estimate of the number of muons needed for a full calibration shows that approximately one day of normal data-taking is sufficient to collect the required statistics.