Combined analysis of KamLAND and Borexino neutrino signals from Th and U decays in the Earth's interior

TL;DR

This study combines data from KamLAND and Borexino to analyze Earth's natural radioactive decay signals, providing insights into Earth's interior composition and disfavoring high-power georeactors.

Contribution

It offers a combined analysis of geoneutrino data from two experiments, constraining Earth's Th and U decay rates and Th/U ratio with improved statistical significance.

Findings

Rejects no geoneutrino signal hypothesis at 5 sigma

Provides bounds on Th+U geoneutrino rates consistent with Earth models

Disfavors Earth's core georeactors exceeding a few TW in power

Abstract

The KamLAND and Borexino experiments have detected electron antineutrinos produced in the decay chains of natural thorium and uranium (Th and U geoneutrinos). We analyze the energy spectra of current geoneutrino data in combination with solar and long-baseline reactor neutrino data, with marginalized three-neutrino oscillation parameters. We consider the case with unconstrained Th and U event rates in KamLAND and Borexino, as well as cases with fewer degrees of freedom, as obtained by successively assuming for both experiments a common Th/U ratio, a common scaling of Th+U event rates, and a chondritic Th/U value. In combination, KamLAND and Borexino can reject the null hypothesis (no geoneutrino signal) at 5 sigma. Interesting bounds or indications emerge on the Th+U geoneutrino rates and on the Th/U ratio, in broad agreement with typical Earth model expectations. Conversely, the results disfavor the hypothesis of a georeactor in the Earth's core, if its power exceeds a few TW. The interplay of KamLAND and Borexino geoneutrino data is highlighted.