The ATLAS SCT alignment system and a comparative study of misalignment at CDF and ATLAS

A promising new frontier in particle physics will soon be accessible at the Large Hadron Collider. The ATLAS experiment will exploit this opportunity to explore the nature of electroweak symmetry breaking and search for physics beyond the Standard Model. The accurate alignment of the ATLAS tracking detector will be crucial for appropriate sensitivity to discovery and precision physics. The challenge of aligning the colossal tracking detector of ATLAS has stimulated the development of a novel alignment system, based on a geodetic grid of over eight hundred length measurements between nodes attached to the detector support structure. This thesis contributes to these developments in three main ways: - Important improvements to the reliability, precision and scope of the system's essential interferometric length measurement technique (FSI) have been demonstrated. A 170 mm stabilized interferometer has been measured to 7 nm. The precision achieved with prototype interferometers of the same design as for ATLAS, is a factor of 5 better than required. - The first prototype FSI grids of multiple, simultaneous length measurements have been constructed and rigorously tested. A method of precisely reconstructing the shape of these grids has been developed. This method has been verified with real measurements by exploiting the redundancy in the grid. - Detailed simulations of the ATLAS SCT alignment system predict it should be capable of reconstructing the SCT shape to within the required precision. A grid design for the SCT End-cap has been developed. Additionally, misalignments in CDF II were evaluated and mapped onto ATLAS to provide an indicative estimate of ATLAS commissioning misalignments. These studies predict misalignment induced momentum degradation will be significant for pT >~ 30 GeV/c^2 and the b-tagging performance will be degraded by at least 10%. The SCT alignment system will play a vital role in ATLAS.