The Xenoscope project addresses the nature of dark matter in our Universe, and the fundamental nature of neutrinos. While we have ample evidence for the existence and distribution of dark matter, its composition at the microscopic level is not known. In the case of neutrinos, we know from neutrino oscillation experiments that they have mass, however the absolute mass scale, as well as their nature (Majorana versus Dirac particles) are unknown.
Xenoscope is focussing on essential, cutting-edge research towards the DARWIN experiment, which can address these question. DARWIN will be a multi-purpose observatory using a multi-ton liquid xenon (LXe) Time Projection Chamber (TPC), with the direct detection of dark matter as its primary goal. This detector aims to achieve an unprecedented sensitivity that will be limited by the irreducible background of neutrino interactions. However, neutrinos themselves are also an interesting physics channel for DARWIN. With a lower energy threshold than current neutrino experiments and its ultra low background level, DARWIN will be sensitive to low energy solar neutrinos (pp, 7Be), as well as to the neutrinoless double beta decay of 136-Xe. Other rare-event searches will include coherent neutrino scattering of solar 8-B and galactic supernova neutrinos and the observation of solar axions, as well as axion-like-particles and dark photons as dark matter candidates.
To design and construct a 50 t (40 t in the time projection chamber, TPC) detector, a number of critical technological challenges must first be addressed. Fundamental aspects are related to the design of the TPC, including the identification of new photosensors, the optimisation of the light and charge collection, and the minimisation of radioactive backgrounds. Xenoscope aims to address these aspects through a number of small, medium-size and a full-scale (in the z-coordinate of the TPC) prototypes. The goal is to specify the required input for the technical design of the 50 t detector.
Arrays of VUV-sensitive SiPMs will be studied as alternative light sensors to photomultiplier tubes, and the signal detection will be optimised for both low and high-energy readout, thus drastically increasing the dynamic range of a LXe-TPC. Low-background materials will be identified and characterized not only for the photosensors and their read-out, but for all the components of the detector. Finally, a full scale TPC in the z-dimension, 2.6 m in height, will be designed, built and operated. The main goal is to demonstrate electron drift and extraction into the vapour phase over the distance relevant for the final DARWIN geometry.
