Design of a compact photon detection system for the PANDA Disc DIRC prototype

Abstract

The existing Gesellschaft für Schwerionenforschung (GSI) in Darmstadt will be upgraded substantially into the Facility for Antiproton and Ion Research (FAIR). The PANDA (antiproton annihilations at Darmstadt) experiment will be one corner stone of the scientific research at FAIR. An antiproton beam with unreached momentum resolution and luminosity will be used in order to probe fundamental constituents of matter. The ambitious physics goals of PANDA can only be reached with state-of-the-art detector technology which will be used to analyze the final state particles originating from the microscopic antiproton reactions. The Endcap Disc DIRC (EDD) fulfills the specific task of improving the particle identification power of the multi-purpose PANDA detector. Specifically, the separation of pions and kaons with high momenta has to be achieved. DIRC stands for Detection of Internally Reflected Cherenkov light, a technique that identifies charged particles by means of measuring their Cherenkov angle which can be inferred from the position and time of impact of single quanta of Cherenkov light.This thesis introduces the reader into the technical challenges which have to be overcome in order to design and build a compact and fast photon detection system for the PANDA EDD. It is also shown, that appropriate optoelectronic equipment exists, that allows to realize the detector concept of the EDD as far as the photon readout is concerned.In a first step microchannel-plate photomultiplier tubes (MCP-PMTs) are tested with a fully automated test setup. Their electronic output is studied under illumination with a well-collimated laser source operated in single-photon mode. This concept is expanded in a second setup which allows to create a magnetic field with the help of strong permanent magnets. Testing in the presence of magnetic fields is important because changes in the performance of the MCP-PMTs have to be anticipated once they are operated in the strong field of the PANDA solenoid magnet. The experiments show that magnetic fields have a strong influence on the imaging characteristics of the sensors. The main reasons for these changes are the displacement and collimation of primary and secondary electrons caused by the Lorentz force. An analysis reveals that an appropriate layout of the anode geometry and orientation of the sensor with respect to the field lines can exploit these changes and lead to an overall improvement as far as the readout of the EDD is concerned. In order to test the sensors at strong fields (up to 800 mT), a test setup was developed to operate and illuminate the sensors between the pole shoes of a strong dipole magnet.A concept for the electronic readout of the sensors was developed in parallel to the testing of the MCP-PMTs. The commercially available TOFPET-ASICs (Time Of Flight, Positron Emission Tomography, Application Specific Integrated Circuit) was thoroughly tested in the setups for MCP-PMTs. Ultimately, the complete photon readout has been integrated into the latest EDD prototype and was tested in a testbeam campaign at the Deutsches Elektronensynchrotron (DESY) in Hamburg. The performance that could be achieved with the close-to-final detector underlines the suitability of the selected components and shows that the combination of MCP-PMTs with the TOFPET ASIC is a suitable option to measure single Cherenkov photons with the necessary spatial and temporal resolution.