Novel Photosensors for Direct Dark Matter Detection

This thesis presents some of the work I have done during the first three years of my Ph.D. studies at Stockholm university and as a member of the XENON collaboration. A full photomultiplier tube (PMT) testing run of 14 PMTs for potential replacement in the XENONnT electrode upgrade is presented. Out of the 14 PMTs one PMT could not be tested properly due to problems with the testing facility. For the other PMTs the gain and dark count measurements were within specifications. One PMT showed medium argon afterpulse, however these were not strong enough to completely disqualify it. In total, all but one PMTs passed the test and the PMT that did not pass was not due to issues with the PMT itself. Furthermore, results of the study of the novel ABALONE photosensor are presented. The gain, dark count, and afterpulse measurements all met expectations. However, serious problems with the stability of the supply voltage make it an unlikely candidate for future dark matter detectors. In the last part my work of monitoring the afterpulse rates in the PMTs in XENONnT is presented. While there were 4 PMTs that showed a significant increase in afterpulse rates, these were still within the safe margin and no PMTs had to be excluded from the analysis due to high rates.