BELLE II. Pixel detector, software and first data analyses. Final report

The funding project 05H19MGKB1 was carried out in the Belle II research network in close collaboration and coordination with the network partners. For the upgrade of the Belle II detector, a new pixel detector was developed using DEPFET technology, which is designed to precisely measure the tracks of charged particles in the immediate vicinity of the interaction point. After a test phase in 2018, in which 4 pixel modules were installed in the experiment, the PXD was put into operation at the beginning of the funding period and has been running successfully in the Belle II experiment ever since. The focus of activities in Göttingen during the reporting period of the funding period was on three sub-aspects: Systematic investigations of the irradiation of final modules in order to reproduce the shifts in threshold voltages measured at the KEK. For this purpose, modules were gradually irradiated with a total dose of 200 kGray, which corresponds to the expected dose of around 7-10 years. A test beam campaign in the electron beam at DESY confirmed that the irradiation does not impair the efficiency of the module if the gate voltage is correctly optimized. The working group developed a cross-calibration method to determine the total ionizing dose using the pixel data and the data from the diamond sensors of the beam monitoring. It was shown that the latter significantly underestimated the radiation dose. - Göttingen developed the Slow Control software for calibrating the pixel modules. This was further developed so that the entire process is automated, which also allows non-experts to take over detector layers. - First analyses of the Belle II data with regard to semileptonic B decays. - Successful completion with publications of the last Belle data analyses. In summary, it can be stated that the goals set were achieved in the reporting period. Despite the difficulties due to the pandemic, the PXD was operated successfully.