Comprehensive geoneutrino analysis with Borexino

Abstract

This paper presents a geoneutrino measurement using 3262.74 days of data taken with the Borexino detector at LNGS in Italy. By observing $52.6_{-8.6}^{+9.4}(\mathrm{stat}{)}_{-2.1}^{+2.7}(\mathrm{sys})$ geoneutrinos (68% interval) from ${}^{238}$U and ${}^{232}$Th, a signal of $47.0_{-7.7}^{+8.4}({\mathrm{stat})}_{-1.9}^{+2.4}(\mathrm{sys})$ TNU with ${}_{-17.2}^{+18.3}$% total precision was obtained. This result assumes the same Th/U mass ratio found in chondritic CI meteorites but compatible results were found when contributions from ${}^{238}$U and ${}^{232}$Th were fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a signal from the mantle is excluded at a 99.0% C.L. when exploiting the knowledge of the local crust. Measured mantle signal of $21.2_{-9.0}^{+9.6}(\mathrm{stat}{)}_{-0.9}^{+1.1}(\mathrm{sys})$ TNU corresponds to the production of a radiogenic heat of $24.6_{-10.4}^{+11.1}$ TW (68% interval) from ${}^{238}$U and ${}^{232}$Th in the mantle. Assuming 18% contribution of ${}^{40}$K in the mantle and $8.1_{-1.4}^{+1.9}$ TW of radiogenic heat of the lithosphere, the Borexino estimate of the total Earth radiogenic heat is $38.2_{-12.7}^{+13.6}$ TW, corresponding to a convective Urey ratio of 0.78${}_{-0.28}^{+0.41}$. These values are compatible with different geological models, however there is a 2.4$\ddot{I}ƒ$ tension with those which predict the lowest concentration of heat-producing elements. By fitting the data with a constraint on the reactor antineutrino background, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW at 95% C.L. is excluded. Particular attention is given to all analysis details, which should be of interest for the next generation geoneutrino measurements.

69 pages, 56 Figures (some composed of multiple files), 17 Tables, 135 References