Evolution of silicon sensor parameters of the CMS tracker due to continuous irradiation during operation

In the near-beam environment of the Large Hadron Collider, the tracker of the CMS experiment is exposed to high radiation levels. Depending on their position with respect to the interaction point, where the particle collisions take place, the silicon detectors were designed to withstand fluences of 10^{14} to 10^{15} MeV neq/cm2. Microscopic radiation-induced damage in the silicon sensors has important consequences on the evolution of sensor parameters like charge collection efficiency, full depletion voltage and leakage current. Inorder to provide a fact base for decisions concerning operational settings, these and other sensor parameters are continuously monitored in both the pixel and strip tracker.The scope of this master’s thesis includes establishing a simulation tool for the pixel tracker that predicts the evolution of leakage current and depletion voltage based on fluence and temperature history. A similar tool for the strip tracker had been developed in 2011 by C. Barth. His work was continued and served as a basis for the pixel tracker modelling tool. The leakage current evolution is modelled according to a well-established empirical model, which describes the evolution with fluence, temperature, and time. The full depletion voltage of the sensors is calculated from an effective charge concentration. The latter was obtained from the Hamburg model. Comparisons of the pixel tracker depletion voltage and leakage current modelling results with available detector data have been performed to obtain a general understanding of the tool and its input parameters. Predictions on the evolution of the detector parameters were performed in close coordination with the monitoring and operation groups of the pixel and strip tracker. Several times during the past year, the results of the tool provided a basis for decisions on detector operation procedures. Both the strip tracker and pixel tracker tools are imparted in a functional state and may contribute to the monitoring and prediction of the leakage current and depletion voltage in the coming years.