hide
Free keywords:
-
Abstract:
The XENON1T experiment is aiming for the direct detection of dark matter in the form of
weakly interacting massive particles (WIMPs) scattering off xenon nuclei. Detecting these
rarely-interacting particles requires an unprecedented low background level. In XENON1T,
the noble gas 222Rn induces the dominant background, either as electronic recoil (ER) background
admixed in the liquid xenon (LXe) volume or as surface background on the Time-
Projection-Chamber’s (TPC) wall. In the first part of this thesis, we constrain the amount of
222Rn induced ER background during the complete run-time of the experiment. We furthermore
survey the considerable 222Rn reduction during the XENON1T operation, resulting in a
final activity concentration of (4:5 ± 0:1) μBq=kg, the lowest one ever achieved in a LXe dark
matter experiment. Conclusions drawn are relevant not only for the interpretation of the background
level in XENON1T, but also for the next-generation experiment XENONnT. The 222Rn
induced surface background can be removed from the PTFE (Polytetrafluoroethylene) wall of
the TPC by dedicated surface cleaning methods based on 32% HNO3. In the second part of
this work, we constructed a small-scale LXe TPC, the HeXe set-up, to test for the first time if a
PTFE surface cleaning based on 32%HNO3 degrades the xenon purity and the performance of
a TPC. No degradation of the xenon purity is observed within the system’s sensitivity, indicating
that 32%HNO3 is a promising candidate for PTFE surface cleaning in LXe TPCs. Our result
lays the groundwork for future research towards confirming that the treatment is applicable in
large-scale LXe detectors.
