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Radon Removal in XENONnT down to the Solar Neutrino Level

E. Aprile ¹, J. Aalbers ², K. Abe ³, S. Ahmed Maouloud ⁴, L. Althueser ⁵, B. Andrieu ⁴, E. Angelino ^6,7, D. Antón Martin ⁸, F. Arneodo ⁹ et al. (XENON Collaboration)

F. Arneodo ⁹, L. Baudis ¹⁰, M. Bazyk ¹¹, L. Bellagamba ¹², R. Biondi ^13,14, A. Bismark ¹⁰, K. Boese ¹³, A. Brown ¹⁵, G. Bruno ¹¹, R. Budnik ¹⁴, C. Cai¹⁶, C. Capelli ¹⁰, J. M. R. Cardoso ¹⁷, A. P. Cimental Chávez ¹⁰, A. P. Colijn ¹⁸, J. Conrad ¹⁹, J. J. Cuenca-García ¹⁰, V. D’Andrea ^7,*, L. C. Daniel Garcia ⁴, M. P. Decowski ¹⁸, A. Deisting ²⁰, C. Di Donato ^21,7, P. Di Gangi ¹², S. Diglio ¹¹, K. Eitel ²², S. el Morabit ¹⁸, A. Elykov ²², A. D. Ferella ^21,7, C. Ferrari ⁷, H. Fischer ¹⁵, T. Flehmke ¹⁹, M. Flierman ¹⁸, W. Fulgione ^6,7, C. Fuselli ¹⁸, P. Gaemers ¹⁸, R. Gaior ⁴, M. Galloway ¹⁰, F. Gao ¹⁶, S. Ghosh ²³, R. Giacomobono ²⁴, R. Glade-Beucke ¹⁵, L. Grandi ⁸, J. Grigat ¹⁵, H. Guan ²³, M. Guida ¹³, P. Gyorgy ²⁰, R. Hammann ¹³, A. Higuera ²⁵, C. Hils ²⁰, L. Hoetzsch ¹³, N. F. Hood ²⁶, M. Iacovacci ²⁴, Y. Itow ²⁷, J. Jakob ⁵, F. Joerg ^13,10,†, Y. Kaminaga ³, M. Kara ²², P. Kavrigin ¹⁴, S. Kazama ²⁷, P. Kharbanda ¹⁸, M. Kobayashi ²⁷, D. Koke ⁵, A. Kopec ^26,‡, H. Landsman ¹⁴, R. F. Lang ²³, L. Levinson ¹⁴, I. Li ²⁵, S. Li ²⁸, S. Liang ²⁵, Z. Liang ²⁸, Y.-T. Lin ¹³, S. Lindemann ¹⁵, M. Lindner ¹³, K. Liu ¹⁶, M. Liu^1,16, J. Loizeau ¹¹, F. Lombardi ²⁰, J. Long ⁸, J. A. M. Lopes ^17,§, T. Luce ¹⁵, Y. Ma ²⁶, C. Macolino ^21,7, J. Mahlstedt ¹⁹, A. Mancuso ¹², L. Manenti ⁹, F. Marignetti ²⁴, T. Marrodán Undagoitia ¹³, K. Martens ³, J. Masbou ¹¹, E. Masson ⁴, S. Mastroianni ²⁴, A. Melchiorre ^21,7, J. Merz ²⁰, M. Messina ⁷, A. Michael⁵, K. Miuchi ²⁹, A. Molinario ⁶, S. Moriyama ³, K. Morå ¹, Y. Mosbacher¹⁴, M. Murra ^1,5,∥, J. Müller ¹⁵, K. Ni ²⁶, U. Oberlack ²⁰, B. Paetsch ¹⁴, Y. Pan ⁴, Q. Pellegrini ⁴, R. Peres ¹⁰, C. Peters²⁵, J. Pienaar ^8,14, M. Pierre ¹⁸, G. Plante ¹, T. R. Pollmann ¹⁸, L. Principe ¹¹, J. Qi ²⁶, J. Qin ²⁵, D. Ramírez García ¹⁰, M. Rajado ¹⁰, R. Singh ²³, L. Sanchez ²⁵, J. M. F. dos Santos ¹⁷, I. Sarnoff ⁹, G. Sartorelli ¹², J. Schreiner¹³, D. Schulte⁵, P. Schulte ⁵, H. Schulze Eißing ⁵, M. Schumann ¹⁵, L. Scotto Lavina ⁴, M. Selvi ¹², F. Semeria ¹², P. Shagin ²⁰, S. Shi ¹, J. Shi¹⁶, M. Silva ¹⁷, H. Simgen ¹³, C. Szyszka²⁰, A. Takeda ³, Y. Takeuchi ²⁹, P.-L. Tan ^19,1, D. Thers ¹¹, F. Toschi ²², G. Trinchero ⁶, C. D. Tunnell ²⁵, F. Tönnies ¹⁵, K. Valerius ²², S. Vecchi ³⁰, S. Vetter ²², F. I. Villazon Solar²⁰, G. Volta ¹³, C. Weinheimer ^5,¶, M. Weiss ¹⁴, D. Wenz ⁵, C. Wittweg ¹⁰, V. H. S. Wu ²², Y. Xing ¹¹, D. Xu ¹, Z. Xu ¹, M. Yamashita ³, L. Yang ²⁶, J. Ye ³¹, L. Yuan ⁸, G. Zavattini ³⁰, and M. Zhong ²⁶ (XENON Collaboration)

¹Physics Department, Columbia University, New York, New York 10027, USA
²Nikhef and the University of Groningen, Van Swinderen Institute, 9747AG Groningen, Netherlands
³Kamioka Observatory, Institute for Cosmic Ray Research, and Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Higashi-Mozumi, Kamioka, Hida, Gifu 506-1205, Japan
⁴LPNHE, Sorbonne Université, CNRS/IN2P3, 75005 Paris, France
⁵Institut für Kernphysik, University of Münster, 48149 Münster, Germany
⁶INAF-Astrophysical Observatory of Torino, Department of Physics, University of Torino and INFN-Torino, 10125 Torino, Italy
⁷INFN-Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, 67100 L’Aquila, Italy
⁸Department of Physics, Enrico Fermi Institute and Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637, USA
⁹New York University Abu Dhabi—Center for Astro, Particle and Planetary Physics, Abu Dhabi, United Arab Emirates
¹⁰Physik-Institut, University of Zürich, 8057 Zürich, Switzerland
¹¹SUBATECH, IMT Atlantique, CNRS/IN2P3, Nantes Université, Nantes 44307, France
¹²Department of Physics and Astronomy, University of Bologna and INFN-Bologna, 40126 Bologna, Italy
¹³Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany
¹⁴Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 7610001, Israel
¹⁵Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
¹⁶Department of Physics and Center for High Energy Physics, Tsinghua University, Beijing 100084, People’s Republic of China
¹⁷LIBPhys, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal
¹⁸Nikhef and the University of Amsterdam, Science Park, 1098XG Amsterdam, Netherlands
¹⁹Oskar Klein Centre, Department of Physics, Stockholm University, AlbaNova, Stockholm SE-10691, Sweden
²⁰Institut für Physik and Exzellenzcluster PRISMA⁺, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
²¹Department of Physics and Chemistry, University of L’Aquila, 67100 L’Aquila, Italy
²²Institute for Astroparticle Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
²³Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
²⁴Department of Physics “Ettore Pancini”, University of Napoli and INFN-Napoli, 80126 Napoli, Italy
²⁵Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
²⁶Department of Physics, University of California San Diego, La Jolla, California 92093, USA
²⁷Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, and Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
²⁸Department of Physics, School of Science, Westlake University, Hangzhou 310030, People’s Republic of China
²⁹Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan
³⁰INFN-Ferrara and Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, 44122 Ferrara, Italy
³¹School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, People’s Republic of China

^*Also at: INFN-Roma Tre, 00146 Roma, Italy.
^†Contact author: florian.joerg@physik.uzh.ch
^‡Now at: Department of Physics and Astronomy, Bucknell University, Lewisburg, Pennsylvania, USA.
^§Also at: Coimbra Polytechnic—ISEC, 3030-199 Coimbra, Portugal.
^∥Contact author: michael.murra@columbia.edu
^¶Contact author: weinheimer@uni-muenster.de

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Phys. Rev. X 15, 031079 – Published 30 September, 2025

DOI: https://doi.org/10.1103/zc1w-88p6

Abstract

The XENONnT experiment has achieved an exceptionally low ${}^{222}{Rn}$ activity concentration within its inner 5.9 tonne liquid xenon detector of $(0.90 \pm 0.02 stat \pm 0.07 syst) μ Bq {kg}^{- 1}$ , equivalent to about 430 ${}^{222}{Rn}$ atoms per tonne of xenon. This was achieved by active online radon removal via cryogenic distillation after stringent material selection. The achieved ${}^{222}{Rn}$ activity concentration is 5 times lower than that in other currently operational multitonne liquid xenon detectors engaged in dark matter searches. This breakthrough enables the pursuit of various rare event searches that lie beyond the confines of the standard model of particle physics, with world-leading sensitivity. The ultralow ${}^{222}{Rn}$ levels have diminished the radon-induced background rate in the detector to a point where it is for the first time comparable to the solar neutrino-induced background, which is poised to become the primary irreducible background in liquid xenon-based detectors.

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synopsis

Dark-Matter Sensitivity Improved with a Xenon Still

Published 30 September, 2025

The most troublesome contaminant in dark-matter searches that use xenon can be removed using a centuries-old concept.

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Why construct a massive, 10 tonne liquid xenon detector operating at a frigid 178 K deep underground? Scientists are on the hunt for incredibly rare particle interactions that could unveil the nature of dark matter. However, tiny amounts of natural radioactivity generate background noise that can obscure these faint signals. The XENONnT experiment has made significant progress by dramatically reducing one of the most troublesome contaminants: radon.

The detector’s ability to uncover new physics hinges on exceptional purity of the liquid xenon. Even trace amounts of dissolved radon can produce light flashes that mimic the sought-after signals. Since radon is a by-product of long-lived isotopes dating back to the early solar system, it is found in nearly all materials, accounting for a significant portion of the natural radiation exposure to humans. To combat this issue, the XENONnT team developed a cryogenic distillation system that continuously purifies the xenon, specifically targeting radon. This process achieves a concentration of about 430 radon atoms per tonne of liquid xenon. Remarkably, the detector’s radioactivity from radon is only 1 billionth of the radioactivity found in a human body and is even lower than the neutrino background from the sun.

This achievement is crucial for the future of low-background science. It demonstrates the potential of advanced purification techniques, paving the way for larger, more sensitive detectors. By creating such a radio-pure environment, XENONnT brings the field closer to uncovering dark matter and exploring new frontiers in particle physics.

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References (55)

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Phys. Rev. X 15, 031079– Published 30 September, 2025

Vol. 15, Iss. 3 — July - September 2025

Received 29 April 2025
Revised 21 July 2025
Accepted 5 August 2025

DOI: https://doi.org/10.1103/zc1w-88p6

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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Radon Removal in XENONnT down to the Solar Neutrino Level

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Physics Subject Headings (PhySH)

synopsis

Dark-Matter Sensitivity Improved with a Xenon Still

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