Low radon and low internal radioactivity for dark matter and rare event xenon detectors

Introduction

The astrophysical and cosmological evidence that the majority of matter in the universe must consist of exotic dark matter is overwhelming. But it is not yet clear what dark matter really is. Very promising candidates are WIMPs, the detection of which would also solve other pressing questions in particle physics.

Detection Methods

For the search for WIMPs, liquid xenon-based detectors are by far the most sensitive. The collaborations LZ, XENON, and DARWIN joined to build a next generation detector, DARWIN/G3, with a sensitivity limited only by coherent neutrino scattering. Such a detector will not only search for dark matter, but will become an observatory for rare event searches, including:

• Axions
• Solar neutrinos
• Neutrinoless double beta decay
• Other rare events

Challenges in Detection

Despite construction in underground laboratories and with further shielding or veto systems for muons or neutrons, the sensitivity of these detectors is limited by radioactive decays within the xenon. This is especially true for the radioactive noble gas isotopes 222Rn and 85Kr, which dominate the background of current xenon-based dark matter experiments.

Project Goals

In this project, we want to push the possibilities of cryogenic distillation to continuously reduce 222Rn and 85Kr to an unprecedented level of:

• 1 atom per 100 mol of xenon (10 mol in the case of 85Kr)

This reduction will make their background contributions at DARWIN/G3 a factor of 10 smaller than that of the un-shieldable solar neutrinos.

Innovative Solutions

Our cryogenic distillation setups, which obtain their cooling power from a novel heat pump concept, offer the additional benefit of determining the impurity concentrations in-situ. We will integrate the novel distillation systems with the removal of electronegative impurities and their diagnostics into a compact cleaning system.

Objectives of LowRAD

Within LowRAD, we aim to provide a complete quasi loss-less continuous 85Kr removal system ready for DARWIN/G3. In addition, we will explore how several important physics channels would become possible due to the extremely low 222Rn and 85Kr concentrations.