Low-mass Dark Matter search with the XENON100 experiment

It is hypothesized that 26% of the mass and energy content of the universe consists of Dark Matter. The most promising Dark Matter candidates are Weakly Interacting Massive Particles (WIMP). If WIMPs are the Dark Matter particles, then they could be directly de-tected via their scattering off nuclei. The XENON100 experiment aims to detect the scattering of a WIMP with a xenon nucleus. This experiment is a xenon-based dual-phase (liquid-gas) Time Projection Chamber (TPC). The interaction of a particle in the TPC produces both scintillation photons and ionization electrons, which are both detected as light signals by photomultipliers.
So far, the XENON100 experiment has not observed WIMPs, and exclusion limits have been produced. The data analysis relies on an accurate description of the backgrounds. In this thesis I present an analysis that assumes potentially unknown backgrounds to be present in the data. In this way, a WIMP exclusion limit without background subtraction is calculated with a minimum WIMP-nucleon cross section of 2.05 × 10^-45 cm² at a WIMP mass of 50 GeV.
Furthermore, I developed a new method to enhance the sensitivity of the XENON100 experiment towards low-mass WIMPs using solely the ionization signal to calculate the recoil energy. Using this method, the sensitivity of the XENON100 experiment is improved by several orders of magnitude for WIMP masses below 7 GeV, excluding a WIMP-nucleon cross section of 1.4 × 10^-41 cm2 at a WIMP mass of 6 GeV.