Spectroscopy of geo-neutrinos from 2056 days of Borexino data

Abstract

We report an improved geo-neutrino measurement with Borexino from 2056 days of data taking. The present exposure is $(5.5\pm 0.3)\times 10^{31}$ proton$\times$yr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain $23.7_{-5.7}^{+6.5}(stat{)}_{-0.6}^{+0.9}(sys)$ geo-neutrino events. The null observation of geo-neutrinos with Borexino alone has a probability of $3.6\times 10^{-9}$ (5.9$\ddot{I}ƒ$). A geo-neutrino signal from the mantle is obtained at 98\% C.L. The radiogenic heat production for U and Th from the present best-fit result is restricted to the range 23-36 TW, taking into account the uncertainty on the distribution of heat producing elements inside the Earth.

4 pages, 4 figures