Observation of geo neutrinos

"Geo-neutrinos, electron anti-neutrinos produced in β decays of naturally occurring radioactive isotopes in the Earth, are a unique direct probe of our planet’s interior. We report the first observation at morethan 3σ C.L. of geo-neutrinos, performed with the Borexino detector at Laboratori Nazionali del GranSasso. Anti-neutrinos are detected through the neutron inverse β decay reaction. With a 252.6 ton yr fiducial exposure after all selection cuts, we detected 9.9+4.1 (+14.6 ) geo-neutrino events, with errors −3.4 −8.2 corresponding to a 68.3% (99.73%) C.L. From the ln L profile, the statistical significance of the Borexino geo-neutrino observation corresponds to a 99.997% C.L. Our measurement of the geo-neutrinos rate is 3.9+1.6 (+5.8 ) events/(100 ton yr). The observed prompt positron spectrum above 2.6 MeV is compatible with that expected from European nuclear reactors. Our measurement of reactor anti-neutrinos excludes the non-oscillation hypothesis at 99.60% C.L. This measurement rejects the hypothesis of an active geo-reactor in the Earth’s core with a power above 3 TW at 95% C.L."