Calibration, Alignment and Long-Term Performance of the CMS Silicon Tracking Detector

Erik Butz
Feb 2009

Thesis Type:

With an active area of more than 200 m², the CMS silicon strip detector is the largest silicon tracker ever built. It consists of more than 15,000 individual silicon modules which have to meet very high standards in terms of noise behavior and electronic crosstalk, as well as their exact positioning within the tracker. Furthermore, the modules will be exposed to a harsh radiation environment over the lifetime of the tracker. This thesis deals with several of the above-mentioned aspects.

In the first part, individual modules are investigated using a testbeam. Some of the modules were irradiated up to an integrated dose which corresponds to the expected one over the life time of the tracker. These modules are investigated with respect to their signal-to-noise behavior, and their cross-talk. Several operational parameters are varied, such as the temperature and the bias voltage. It is shown that the modules behave as expected. The signal-to-noise ratio is well above the specifications and the cross-talk increases only very moderately with irradiation. Furthermore, the spatial resolution of the modules is investigated. Different cluster algorithms are utilized and compared. It is shown that the spatial resolution is not much affected by irradiation and that the spatial resolution can be improved with respect to the current standard reconstruction.

In the second part, larger structures of the silicon tracker are studied during the so-called "tracker slice-test". Two sectors from one of the tracker end caps are investigated. Special emphasis is given to the commissioning of the system and the monitoring of the various commissioning parameters. Furthermore, the noise of the system is investigated as a function of the ambient temperature and different powering schemes. It is shown that the noise of the system behaves as expected. The noise is stable within 2 % for different powering schemes. Also possible failures of components are investigated and persistent defects are identified and monitored. The total amount of localized and non-localized defects is found to be about 0.7 % for the two end cap sectors.

Lastly, the alignment of the detector is a subject of interest, as the exact alignment of all components of the tracker with respect to each other will be of prime importance for any analysis using the tracker. The separation of primary and secondary vertices as well as the momentum resolution depend largely on a very good alignment of the detector. In this thesis, the validation of an alignment result is investigated. Several quantities which could be used to judge the quality of an alignment are discussed. A first application of the validation is shown on cosmic muon data, taken with the whole silicon tracker after the integration into the experiment.

PDF icon Erik_Butz.pdf4.07 MB