Scintillation light detection in XENON1T: Photosensor tests and light collection simulations

The experiment XENON1T aims at directly detecting dark matter via interactions of weakly interacting massive particles (WIMPs) with xenon nuclei. The goal of XENON1T is to improve the sensitivity compared to its predecessor experiment XENON100 by 2 orders of magnitude by using a larger xenon volume and by reducing the amount of background events. The XENON1T inner detector, which contains 2:2 t of liquid xenon, will be equipped with 248 photomultiplier tubes (PMTs) to detect the scintillation light induced by a possible WIMP interaction. For this purpose 3 00 R11410-21 PMTs with low intrinsic radioactivity and high quantum eciency are being manufactured by Hamamatsu. One part of this thesis describes the tests of the rst 90 R11410-21 PMTs. Important features like the dark count rate and the gain were measured at room- and liquid xenon temperature. The second part of this thesis is dedicated to investigating the scintillation light propagation and the light collection eciency (LCE) in a XENON1T-like detector. A Monte Carlo simulation based on GEANT4 was developed to test how dierent assignments of quantum eciency (QE) values to the PMT positions aect the LCE. In a rst approach, it is found that optimizing the PMT arrangement, considering the QE values, can enhance the LCE value by a factor of 7% at most, which would result in a 7% higher light yield for XENON1T