Abstract
Puzzles exist in our theories of Earth’s formation and bulk chemical composition. Related to these questions is our incomplete knowledge of the planet’s overall heat budget and thermal history. The successful observation of geoneutrinos originating from uranium and thorium decay chains, manifestations of the planet’s natural radioactivity, serves as the only direct probe of Earth’s internal, radiogenic heat engine so far. Intriguingly, potassium (40K) geoneutrinos have never been observed and have so far been considered impractical to measure despite their importance in Earth’s radioactive inventory. We propose here an approach for potassium geoneutrino detection that exploits their antiparticle nature. The detection framework relies on the LiquidO technique to identify positrons, thereby reducing otherwise overwhelming backgrounds. Antineutrino interactions with candidate isotope targets have been thoroughly examined and copper is found to be the ideal isotope able to meet all experimental feasibility conditions. We discuss the challenging experimental requirements to yield a potassium geoneutrino discovery.
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Acknowledgements
We acknowledge the support received from: (i) the ‘Chaire Internationale de Recherche Blaise Pascal’ (Laureate 2016: F. Suekane), financed by Région Île-de-France (Paris) and coordinated by the Fondation de l’École Normale Supérieure (Paris) and hosted by CNRS at the APC Laboratory (Paris). This funding enabled launching the pioneering studies, including supporting a dedicated postdoctoral research fellow (S. Wagner) whose studies, input and comments were critical; (ii) ‘L’Instituto Universitario de Studi Superiori-Ferrara 1391’ for supporting Copernicus Visiting Scientist (Laureate 2019: M. Chen) and hosted by the Università di Ferrara and INFN Ferrara during the key phase of this study; and (iii) the ‘Emilie du Châtelet’ Programme, financed by the P2IO (LabEx, Université Paris-Saclay, France) supporting visiting scientist (2022: M. Chen) hosted at the IJCLab during the final writeup phase of this publication. We also thank Prof C. Volpe (APC, Paris) for helpful discussions regarding nuclear physics input for neutrino cross sections. The authors pay tribute to Prof Giovanni Fiorentini for his pioneering studies on geoneutrinos. Although he passed away in June 2022, his memory remains vibrant in our minds.
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The primary authors for this work have been listed first (alphabetically), followed by all other LiquidO Consortium members (alphabetically). The primary authors were fully involved in the conception and execution of this study, including performing calculations, interpretation of results, evaluation of the scientific and technical considerations, development of the discussion and formulation of conclusions, and writing the paper. Consortium members were variously involved in developing LiquidO as a new idea and detection technique, including software for simulations. All authors reviewed and approved the submitted manuscript.
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LiquidO Collaboration. Probing Earth’s missing potassium using the antimatter signature of geoneutrinos. Commun Phys (2026). https://doi.org/10.1038/s42005-026-02518-6
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DOI: https://doi.org/10.1038/s42005-026-02518-6
