Innovative Technology Pushes the Boundaries of Ultra-Low Background Physics. In the global search for dark matter, the XENONnT experiment at the INFN Laboratori Nazionali del Gran Sasso (LNGS) stands out as one of the world's most sensitive detectors in the field. Th2 international collaboration, comprising over 190 scientists from 30 institutions worldwide, has achieved a major technological breakthrough: a significant reduction in radioactive background noise, a feat never previously achieved in rare-event physics experiments.
The core of this innovation is a cryogenic distillation system that purifies the liquid xenon inside the detector. The new system has reduced radon-induced radioactivity to an extraordinarily low level: a billion times lower than the natural radioactivity of the human body and a factor of four lower than the previous record level in XENONnT. This achievement is crucial for detecting the extremely faint signals in xenon-based detectors from rare particle interactions that could reveal the nature of dark matter.
The XENONnT detector aims at measuring the interactions of hypothetical dark matter particles with xenon atoms. Shielded deep underground from cosmic rays and maintained at -95 °C to keep xenon in its liquid state, the detector requires an environment with virtually no contamination. However, even trace amounts of radon can create false signals, obscuring the rare events scientists are looking for.
The new distillation column continuously purifies the xenon, lowering the radon concentration down to just 430 radon atoms per tonne of liquid xenon, making their background contribution as low as that from solar neutrinos. This sets a new benchmark for purity in xenon-based detectors and dramatically enhances sensitivity to rare particle interactions.
"This achievement demonstrates the effectiveness of international collaboration," says Prof. Christian Weinheimer from the University of Münster, whose team led the development of this technology. "This breakthrough allows us to push the limits of particle physics and get one step closer to solving the mystery of dark matter."
The Collaboration's full evaluation of this lowest radon background rate ever achieved is accepted for publication in Physical Review X this month.
Original publication
Aprile E. et al. (2025): Radon Removal in XENONnT down to the Solar Neutrino Level. Physical Review X 15, 031079 (https://journals.aps.org/prx/abstract/10.1103/zc1w-88p6).
REIS - 01.10.2025