Studies for the Commissioning of the CERN CMS Silicon Strip Tracker

In 2008 the Large Hadron Collider (LHC) at CERN will start producing proton-proton collisions of unprecedented energy. One of its main experiments is the Compact Muon Solenoid (CMS), a general purpose detector, optimized for the search of the Higgs boson and super symmetric particles. The discovery potential of the CMS detector relies on a high precision tracking system, made of a pixel detector and the largest silicon strip Tracker ever built. In order to operate successfully a device as complex as the CMS silicon strip Tracker, and to fully exploit its potential, the properties of the hardware need to be characterized as precisely as possible, and the reconstruction software needs to be commissioned with physics signals. A number of issues were identified and studied to commission the detector, some of which concern the entire Tracker, while some are specific to the Tracker Outer Barrel (TOB): - the time evolution of the signals in the readout electronics need to be precisely measured and correctly simulated, as it affects the expected occupancy and the data volume, critical issues in high-luminosity running; - the electronics coupling between neighbouring channels affects the cluster size and hence the hit resolution, the tracking precision, the occupancy and the data volume; - the mechanical structure of the Rods (the sub-assemblies of the TOB) is mostly made of carbon fiber elements; aluminum inserts glued to the carbon fi ber frame provide efficient cooling contacts between the silicon detectors and the thin cooling pipe, made of a copper-nickel alloy; the different thermal expansion coefficients of the various components induce stresses on the structure when this is cooled down to the operating temperature, possibly causing small deformations; a detailed characterization of the geometrical precision of the rods and of its possible evolution with temperature is a valuable input for track reconstruction in CMS. These and other issues were studied in this thesis. For this purpose, a large scale test setup, designed to study the detector performance by tracking cosmic muons, was operated over several months. A dedicated trigger system was set up, to select tracks synchronous with the fast readout electronics, and to be able to perform a precise measurement of the time evolution of the front-end signals. Data collected at room temperature and at the Tracker operating temperature of -10‰°C were used to test reconstruction and alignment algorithms for the Tracker, as well as to perform a detailed qualification of the geometry and the functionality of the structures at different temperatures.