A position sensitive photon detector for the CLAS12 ring imaging Čerenkov application

The upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) to CLAS12 will offer unique possibilities to study the strong interaction and the internal nucleon dynamics. For this, excellent hadron identification over its full kinematic range is essential and a Ring Imaging CHerenkov detector (RICH) has been proposed for installation into CLAS12 to achieve this. This thesis describes studies performed towards the selection of a photon detector for use in the CLAS12 RICH, which will be a crucial component for the success of the RICH performance. MultiAnode PhotoMultiplier Tubes (MAPMTs) have been selected as the most promising photon detectors for the CLAS12 RICH. A high-precision laser test-stand was developed to characterise candidate MAPMTs and the results were used to determine the Hamamatsu H8500 MAPMT as the optimal device. Throughout the laser tests the H8500 MAPMT proved to be single photon sensitive as demanded, the spatial resolution was found to satisfy the required value of less than 1cm by 1cm and the device exhibited sufficiently low crosstalk levels of less than 3%. The response and crosstalk of the device showed a dependency upon the MAPMT construction, the magnitude of which was shown to be negligible and overall the H8500 provides a plane of suitable uniformity to satisfy the imaging functionality of the CLAS12 RICH. To further confirm the H8500 MAPMT choice, its performance in response to Cherenkov light within two prototype setups was evaluated. First a small-scale prototype was designed and constructed, incorporating one H8500 MAPMT to image Cherenkov rings created by cosmic muons traversing aerogel radiators. Extraction of the results required full understanding of the device based upon calibrations made with the laser tests. The prototype was also simulated in detail, allowing for a model description of the MAPMT to be validated. Secondly, 28 H8500 MAPMTs were used in a large-scale prototype to image Cherenkov rings produced by mixed hadrons traversing aerogel radiators, to evaluate their performance in a geometry and an environment similar to that expected in the CLAS12 RICH. Both prototypes revealed that the H8500 MAPMT can be used to successfully detect the required 7 photons per Cherenkov event to achieve pion/kaon separation in the CLAS12 RICH. Furthermore, a pion/kaon separation of more than 3 sigma at 6GeV/c was observed through a preliminary analysis of data extracted with the large-scale prototype. The prototype studies also confirmed the low-noise behaviour of the H8500 MAPMT. As a result of the laser test-stand and prototype tests, the choice of the H8500 MAPMT as the photon detector for the CLAS12 RICH was validated