Teflon reflectivity studies for the XENON1T experiment

Ordinary matter makes up only 5% of the universe as we know it. Out of the remaining 95%, 25% are composed of a new type of matter called dark matter. By looking for the interaction of dark matter particles with liquid xenon and the resulting scintillation, the XENON project attempts to discover dark matter in the form of Weakly Interacting Massive Particles (WIMPs). The current experiment XENON100 has achieved a sensitivity of σ < 2.0 . 10-45 cm2 to the WIMP-nucleon cross section. The experiment now in its next phase, XENON1T, will increase this sensitivity by two orders of magnitude by utilizing about 2.6 tons of xenon as target. In order to have a high scintillation collection to detect the low energy recoils of dark matter interactions, a teflon reflector is used. However, the reflection properties of teflon need to be better understood. For this purpose, a deuterium lamp has been set up, which shines 178 nm light on a teflon sample. The reflected light is then viewed by a movable VUV PMT. This setup allows to measure the specular and diffuse reflectivity of teflon at varying angles of incidence and reflection, allowing for a full model of the reflection process. Screening of different teflon samples will allow for an optimization of the teflon reflector to be used in the XENON1T experiment. Results of these measurements are discussed.