The XENON project is a staged program searching for dark matter by the means of two-phase Liquid Xenon Time Projection Chambers (LXe-TPCs). If dark matter particles exist, they might interact at some level with ordinary matter, opening up the possibility of being detected in specialized ultra-low background detectors. The LXe-TPCs of the XENON family have been deployed at Laboratori Nazionali del Gran Sasso (LNGS). XENON1T, the most recent experiment, featured 2 tonnes of Liquid Xenon as target for dark matter and was operated from 2016 till the end of 2018. It delivered the most stringent up-to-date limit on the WIMP-nucleon coupling and on a wide range of alternative dark matter candidates. Several ongoing analyses promise further results constraining exotic particles and interactions.
Two-phase LXe-TPCs are ideal for rare-event searches that require ultra low-background environments. This technology simultaneously measures the excitation and ionization induced by an interaction in the liquid phase down to 1 keV and the charge and light collection mechanisms enable position reconstruction. The latter allows to restrict the data analysis only to interactions occurring in the central (fiducial) core of the xenon target that features a much reduced background. The background induced by contaminants in the materials surrounding the TPC is effectively suppressed by xenon self-shielding properties (high-Z atoms). This technology combined with the easiness of purifying the xenon gas allow to build multi-tonne detectors capable of running very stably for years and accumulate extremely large ultra-low background exposures that can be used for a variety of dark matter and rare-event searches.
XENON1T has been recently decommissioned in preparation for XENONnT, scheduled to start operations before the end of the year and expected to feature, thanks to its larger mass and lower background, a sensitivity to dark matter about 10 times better than its predecessor.
Luca Grandi
Senior Member