Silicon strip detector qualification for the CMS experiment

The Compact Muon Solenoid (CMS) is one of the four experiments being installed at the Large Hadron Collider (LHC) which is located at the european organization for nuclear research CERN in Geneva. This proton-proton collider will explore a new energy regime of up to 14TeV center-of-mass energy. To provide the best spatial resolution for the particle trajectory reconstruction and a very fast readout, the inner tracking system of CMS is build up of silicon detectors with a pixel tracker in the center surrounded by a strip tracker. The silicon strip tracker consists of so-called modules representing the smallest detection unit of the tracking device. These modules are mounted on higher-level structures called shells in the tracker inner barrel (TIB), rods in the tracker outer barrel (TOB), disks in the tracker inner disks (TID) and petals in the tracker end caps (TEC). The entire strip tracker spans an active area of about 198m2 and consists of approximately 16000 modules. Before the silicon sensors were assembled on the respective substructures they had to pass a qualification test where each single readout channel was checked for its functionality. Only modules with a failure rate of less than 2% were allowed to be integrated in the tracker. In case of the tracker end caps the following petal assembly took place in six so-called Petal Integration Centers whereof one was located in Aachen. Subsequent to the assembly each petal was tested and graded in a longterm test being the first time that all petal components were read out simultaneously and operated in a cold environment. Out of 294 production petals (288 are needed for the two end caps) 286 petals received the best quality grade A. Only about 1h of the TEC readout channels were flagged as faulty in the single module test and the petal longterm test. In summer 2006 the so-called Magnet Test and Cosmic Challenge (MTCC) took place in the CMS assembly hall at CERN. It was the first time that the experiment was closed including parts of all subdetectors. The superconducting solenoid was ramped up to a magnetic field of 4T and parts of the muon system were used to deliver a trigger for cosmic ray muons to all subdetectors. Thus, the performance of the participating two shells of the TIB, four rods of the TOB and two petals of the TEC (representing about 1% of the final strip tracker) could be studied in different magnetic fields over a period of approximately two month using cosmic muon signals. The last test before inserting the tracker in the CMS experiment was the Tracker Slice Test performed in spring/summer 2007 at the Tracker Integration Facility (TIF) at CERN after installing all subdetectors in the tracker support tube. Approximately 25% of the strip tracker +z side was powered and read out using a cosmic ray trigger built up of scintillation counters. In total, about 5 million muon events were recorded under various operating conditions. These events together with results from commissioning runs were used to study the detector response like cluster charges, signal-to-noise ratios and single strip noise behaviour as well as to identify faulty channels which turned out to be in the order of a few per mille. The performance of the silicon strip tracker during these different construction stages will be discussed in this thesis with a special emphasis on the tracker end caps