Probing Earth’s missing potassium using the antimatter signature of geoneutrinos

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. Detection of geoneutrinos from 40K decay in the Earth would yield a wealth of information on Earth’s bulk chemical composition and radiogenic heat. By exploiting the positron identification ability of LiquidO to reject backgrounds, charged-current neutrino capture reactions on 63Cu is proposed as the ideal way to observe potassium geoneutrinos