Erwartete Messung der Z Produktionsrate mit dem CMS Detektor und Simulation des Tracker Laser Alignment Systems

The Large Hadron Collider is a two-ring, superconducting accelerator and collider which can provide both proton and heavy-ion beams. First collisions are foreseen for 2009. The Compact Muon System (CMS) detector will measure the particles created in the hadron collisions and can confirm the Standard Model by establishing the existence of the Higgs boson, but also search for new phenomena. In order to provide a robust and precise track reconstruction, which can already be used in the High-Level Trigger systems, the positions of the silicon sensors in the CMS tracker have to been known with an accuracy of O(100µm). Therefore the CMS tracker has been equipped with a dedicated alignment system. The Laser Alignment System (LAS) aligns the tracker subdetectors with respect to each other and can also monitor the stability of the sensor positions during data taking. This study describes the implementation of a realistic simulation of the LAS in the CMS software framework (CMSSW) as well as the analysis of the first data collected during the integration of one of the tracker endcaps. In the present study it has been found that the alignment of the endcaps is possible with an accuracy of approximately 76µm. These results are in agreement with independent measurements of the TEC geometry using cosmic muons or photogrammetry measurements. The accuracy of approximately 100µm needed for track pattern recognition and reconstruction can be assured by the Laser Alignment System as shown in this study. Accurate knowledge of the luminosity delivered by the LHC to the experiments is an essential ingredient for many physics studies. The present work uses the production of lepton pairs via the Drell-Yan mechanism to determine the integrated luminosity with the CMS detector. A Monte Carlo generator (MC@NLO) including next-to-leading order QCD diagrams has been used to generate Drell-Yan events decaying into two muons. After a full CMS detector simulation, the events have been reconstructed using the CMS software framework (CMSSW). Several sources contributing to the background have been studied as well as various possible sources of systematic uncertainties. The analysis of Drell-Yan muon pairs has proved to be an accurate way to measure the integrated luminosity with the CMS detector.