Backgrounds in XENON1T

We are missing 85% of the matter in our Universe. This simple statement motivates thousands of physicists around the world to search for and explain dark matter. The first observations suggesting the existence of more non-luminous (e.g., dark matter and neutrinos) than luminous matter (e.g., stars, planets and gas) are now about 100 years old. The XENON1T experiment searches for a specific Dark Matter particle candidate, namely the weakly interacting massive particle (WIMP) with a liquid xenon target in an ultra-low background detector.
XENON1T, located at the Laboratori Nazionali del Gran Sasso in Italy, uses 3.2 t of xenon as target material, which is purified and cooled continuously during operation. 248 light detectors are used to measure every particle interaction. To determine if dark matter interactions are found we compare the number of light flashes seen with the number we expect from Monte Carlo simulations.
To have a chance of measuring WIMPs scattering off xenon nuclei, XENON1T was designed and built as an ultra-low background experiment. Monte Carlo simulations show that the main background component in the low energy region is from (naturally occurring) radon. This thesis starts with understanding the process of signal reconstruction and data selection in XENON1T to show its amazing performance. The second part is dedicated to determining the concentration and spatial distribution of the main background component. The last part presents the new, and most stringent, constraints on WIMPs in the space of mass versus cross-section. XENON1T is now proudly world leading in finding nothing.