Speaker
Description
The XENONnT experiment, located underground at the Laboratori Nazionali del Gran Sasso, uses a total of 8.6t of high-purity liquid xenon to directly search for WIMP (weakly interacting massive particle) dark matter using a dual phase time projection chamber. A predominant part of the detector's low-energy background is caused by intrinsic contamination of the xenon with Rn-222, which is continuously emanating from the detector materials. For the reduction of this background, a high-flow online radon removal system was designed and constructed (M. Murra et al., Eur. Phys. J. C 82 (2022) 1104), which uses cryogenic distillation based on the difference in vapor pressure between radon and xenon. The system can be run concurrently in two modes of operation: At a flow rate of 200 slpm, liquid xenon is extracted from the detector and passed through the system, which results in a reduction in radon concentration by a factor of two. An additional flow of 25 slpm of gaseous xenon is extracted from regions with high radon emanation (cables, feed lines, ...) providing another reduction factor of about two. With the combined operation of both modes, an extremely low Rn-222 activity concentration of < 1 µBq/kg is achieved. This unprecedentedly low radon concentration marks a new world record, and sets the bar for the lowest concentration in any xenon dark matter experiment today. This project is supported by BMBF Verbundforschung under 05A20PM1 and 05A23PM1.
