XAMS - development of liquid xenon detector technology for dark matter searches

One of the most promising detector technologies to directly detect weakly interacting massive particle (WIMP) dark matter are time projection chambers (TPCs) filled with dual-phase (liquid and gaseous) xenon. The hypothetical WIMP could scatter with atoms in the liquid and the transferred recoil energy would lead to a prompt light signal (S1) and, after a drift time of ionisation electrons into the gas phase, to a secondary signal (S2). Only a detection of a dark matter particle interaction can provide evidence beyond doubt for its existence and could potentially solve a puzzle that combines astroparticle physics and cosmology. To date, even the most sensitive detectors (filled with more than 100 kg of liquid xenon) could not produce indisputable proof of dark matter. In order to improve the sensitivity of future dual-phase xenon TPCs this thesis investigated the GridPix detector as an alternative for the detection of the S2 signal. Unlike the typically used photomultiplier tubes, GridPix offers a lower radioactive content.
This could reduce the intrinsic background of the TPC, hence making it more sensitive to small energy deposits. However, the studies showed that GridPix does not operate stably enough at the challenging conditions of high-purity, low-temperature gas. To test other detector technologies as well as to study xenon properties and data acquisition techniques, a small-scale dual-phase xenon TPC was built and commissioned at Nikhef: XAMS, a xenon facility at Amsterdam. Calibration measurements showed the basic functioning of the TPC and led to improvements that make XAMS a valuable testing ground for future dark matter search experiments.