Mantle geoneutrinos in KamLAND and Borexino

TL;DR

This study analyzes geoneutrino signals from KamLAND and Borexino to estimate Earth's mantle contribution, finding hints of a residual mantle flux that slightly favors models with higher thorium and uranium abundances.

Contribution

It provides a detailed analysis of crustal and mantle geoneutrino fluxes, improving estimates of Earth's interior composition using combined data from two major experiments.

Findings

Residual mantle geoneutrino flux detected at ~2.4 sigma level.

Crustal flux estimates are refined with state-of-the-art geochemical data.

Mantle flux estimates favor higher Th and U abundances within uncertainties.

Abstract

The KamLAND and Borexino experiments have observed, each at ~4 sigma level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. To this purpose, we analyze in detail the experimental Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino oscillation effects. We estimate the crustal flux at the two detector sites, using state-of-the-art information about the Th and U distribution on global and local scales. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ~2.4 sigma level by combining the KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios with relatively high Th and U abundances, within +-1 sigma uncertainties comparable to the spread of predictions from recent mantle models.