Potassium abundance in the Earth and Borexino data

TL;DR

This study analyzes Borexino data to estimate Earth's potassium abundance, revealing the need for more data and better knowledge of bismuth levels, and discusses prospects for future detectors targeting $^{40}$K geo-neutrinos.

Contribution

It introduces a new analysis including $^{40}$K geo-neutrino scattering and assesses the statistical limitations in measuring Earth's potassium abundance.

Findings

Two equivalent minima found in $$ analysis.

Current data insufficient for definitive potassium measurement.

Future detectors could improve sensitivity to Earth's potassium flux.

Abstract

An independent analysis of Borexino single event energy spectrum of recoil electrons and alphas was carried out. We compared two sets of single event sources. The first set is similar to the one used in Borexino Collaboration analysis. The second set additionally includes the scattering of $^{40}$K-geo-($\bar{\nu} + \nu$) on scintillator electrons. We found two equivalent minima for $\chi^2$ for second set. The one is for total counting rates $R(^{40}$K-geo-$(\bar{\nu} + \nu)) = 0.0$ and $R(^{210}$Bi) = 10 cpd/100t. The other one is for $R(^{40}$K-geo-$(\bar{\nu} + \nu)) = 7.05$ cpd/100t and $R(^{210}$Bi$) = 6$ cpd/100t. We performed MC pseudo-experiments and found that we do not have enough statistics and need to know the bismuth concentration in the scintillator for definite measurement of potassium abundance in the Earth. The possibility of building a next-generation detector for looking for the $^{40}$K-geo-($\bar{\nu} + \nu$) flux is being considered.