Development of Pixel Modules for the Belle II Detector

Abstract

The future Belle II experiment at the SuperKEKB accelerator will improve the current understanding of flavor physics by increasing the recorded data set fiftyfold; allowing high precision measurements of CKM parameters and measurements of rare decays. The experiment will feature 2 layers of ultra-thin DEPFET pixel modules close to the interaction point to increase the vertex resolution while coping with an instantaneous luminosity 40 times higher than the previous Belle experiment. A DEPFET is a <strong>DE</strong>pleted <strong>P</strong>-channel <strong>F</strong>ield <strong>E</strong>ffect <strong>T</strong>ransistor. Charge collected in the depleted bulk drifts into a potential minimum below the transistor gate and modulates the drain current, which is processed by two ASICs, the DCD and DHP. In this thesis the protptype ASICs for Belle II were characterized with an emphasis on the <strong>D</strong>rain <strong>C</strong>urrent <strong>D</strong>igitizer (DCD). To ensure data quality during the experiment runtime of Belle II, the radiation hardness and temperature stability of the DCD was investigated. With characterized ASICs, small and large Belle II prototype sensors were evaluated and used to investigate system performance. Sensor measurements were performed using a laser system with in-pixel resolution, radioactive sources and high energy electron beams at the DESY beam test facility.