Detector Alignment Studies for the CMS Experiment

This thesis presen ts studies related to trac k-based alignmen t for the future CMS exp erimen t at CERN. Excellen t geometric alignmen t is crucial to fully bene t from the outstanding resolution of individual sensors. The large num ber of sensors mak es it dicult in CMS to utilize computationally demanding alignmen t algorithms. A computationally ligh t alignmen t algorithm, called the Hits and Impact Points algorithm (HIP), is dev elop ed and studied. It is based on minimization of the hit residuals. It can be applied to individual sensors or to comp osite objects. All six alignmen t parameters (three translations and three rotations), or their subgroup can be considered. The algorithm is exp ected to be particularly suitable for the alignmen t of the innermost part of CMS, the pixel detector, during its early operation, but can be easily utilized to align other parts of CMS also. The HIP algorithm is applied to sim ulated CMS data and real data measured with a test-b eam setup. The sim ulation studies demonstrate that the algorithm is a promising candidate for the alignmen t of the pixel detector. The test-b eam study sho ws that the use of the algorithm signi can tly impro ves the data measured with gen uine CMS hardw are. The positioning uncertain ties of di eren t parts of CMS have also been systematically esti- mated. Ready-made scenarios corresp onding to these uncertain ties have been implemen ted in the CMS reconstruction soft ware OR CA. These scenarios have been used in the align- men t studies. They have also been widely used for more realistic misalignmen t sim ulation in the physics performance studies of the CMS collab oration.