A New Journey to the Center of the Earth

Abstract: There are still several unanswered fundamental questions concerning our planet and in particular, about the deep Earth, from where we lack direct samples. Today, due to the progress in neutrino-detection techniques, a new and unique tool to study our planet exists: geoneutrinos, antineutrinos from the decays of long-lived radioactive elements inside the Earth. In 2020, the Borexino experiment published its updated geoneutrino measurement. Thanks to the increase in acquired data and the improved analysis techniques in an enlarged fiducial volume, the final precision has significantly improved, corresponding to a total geoneutrino signal of 47.0$^{+8.4}_{-7.7}\,({\rm stat)}^{+2.4}_{-1.9}\,({\rm sys})$ TNU. The null-hypothesis of the geoneutrino signal from the Earth's mantle was excluded at a 99% C.L. for the first time, while exploiting the knowledge of the local crust around the detector. The article will introduce the field and describe the key elements of the updated analysis. Geological interpretation and significance of the new result will be discussed in terms of the corresponding radiogenic heat and the limits to a hypothetical georeactor.