Study of silicon pixel sensors for the ATLAS detector

Test beam characterization of prototypes of ATLAS silicon pixel sensors is discussed. Some of the sensors were irradiated to fluences up to 10**15 n_eq/cm**2. Measurements of charge collection efficiency, particle detection efficiency, depletion depth, Lorentz angle and spatial resolution have been performed. A model to compute the value of Lorentz angle from the charge drift properties in silicon is presented and found to be in agreement with test beam data. The Lorentz angle is found to be dependent on the mean electric field in the sensor, hence it changes varying the applied bias voltage. In the last chapter a study of ATLAS tracking and b-tagging performances is made using the GEANT simulation of the detector. The study is performed for two different algorithms to reconstruct the pixel cluster position and for the different values of the pixel bias voltage.