Integration of the End Cap TEC+ of the CMS Silicon Strip Tracker

At the European Organization for Nuclear Research (CERN) ne ar Geneva the new proton-proton collider ring LHC and the experiments that will be operated a t this accelerator are currently being finalised. Among these experiments is the multi-purpose det ector CMS whose aim it is to discover and investigate new physical phenomena that might become ac cessible by virtue of the high center- of-mass energy and luminosity of the LHC. Two of the most inte nsively studied possibilities are the discovery of the Higgs Boson and of particles from the spectr um of supersymmetric extensions of the Standard Model. CMS is the first large experiment of high- energy particle physics whose inner tracking system is exclusively instrumented with silicon d etector modules. This tracker comprises 15 148 silicon strip modules enclosing the interaction poin t in 10–12 layers. The 1. Physikalisches Institut B of RWTH Aachen was deeply involved in the completi on of the end caps of the tracking system. The institute played a leading role in the end cap des ign, produced virtually all support structures and several important electrical components, d esigned and built the laser alignment system of the tracker, performed system tests and finally int egrated one of the two end caps in Aachen. This integration constitutes the central part of the presen t thesis work. The main focus was on the development of methods to recognise defects early in the integration process and to assert the detector’s functionality. Characteristic quantities suc h as the detector noise or the optical gain of the readout chain were determined during integration as wel l as during a series of tests performed after transport of the end cap from Aachen to CERN. These meas urements show a constantly high quality of the integrated device. The procedures follo wed during the mechanical integration of the detector and during the commissioning of integrated s ectors are explained, and the software packages developed for quality assurance are described. Th is part of the document also covers problems that occured in the course of the integration proce ss. In addition, results of the detector readout are presented. It could be shown that more than 99.5 % of the approximately two million readout channels of the detector are working, that the noise of the silicon modules is below about 2000 electrons and that the common-mode noise is negligible . With these results, reliable signal detection can be expected even towards the end of the foresee n life time of the end cap, when radiation damages will lead to higher noise and reduced sign al charge collection. During the integration phase, sub-structures of the end cap — named petals — were subjected to a reception test which has also been designed and operated as part of this thesis work. The test setup and software developed for the test are introduce d and an account of the analysis of the recorded data is given. Containing about 20 silicon modu les and related readout electronics, petals are the basic building blocks of the end cap system. Th e reception test mainly confirmed the very good quality of petals delivered by external intitu tes and found a small number of defects which could be repaired before integration of the petals int o the end cap. Before the end cap project entered the production phase, a fin al test beam experiment was performed in which the suitability of a system of two fully eq uipped petals for operation at the LHC was checked. In this last step of the system test for the en d caps, stable operation and a good data quality could be verified. The measured ratio of the signal induced in the silicon sensors by minimal ionising particles to the detector noise — in the r eadout mode relevant for operation at design luminosity — was shown to be greater than 20 for all m odule geometries. A software for analysing the recorded data was developed and used in all presented studies. This tool was tuned to the special requirements of the test an d integration phase of the detector.The functionality of the software and the algorithms it uses are explained. A comparison of the different studies demonstrates the const antly high detector quality in setups of individual petals as well as in systems comprising hundreds of silicon modules in the integrated end cap. At the same time, the reproducibility of the measurements could be estab- lished, which is another requirement for successful operat ion of the tracker end caps in the search of new physics at the LHC.