Advances in Neutrino Geophysics

Neutrino Geophysics involves mostly detection and interpretation of the Earth's flux of geoneutrinos, electron antineutrinos (MeV) emitted during natural radioactive decays, with the Th and U flux being the only detectable neutrinos. In addition, higher energy neutrinos can be used to establish the deep Earth's electron density (mostly hydrogen content) using nu oscillation studies at GeV scales and Earth's density structure via nu absorption studies at TeV scales.

Results from KamLAND (Japan) and Borexino (Italy) detectors find an Earth's flux consistent with a 20 to 30 TW Earth and excludes a 10 TW model at the 1 sigma uncertainty level. A combined analysis of KamLAND and Borexino results yield a mantle flux of 9 +/- 6 TNU (or 13TW). The KamLAND detector now assesses independently the contributions from Th and U geoneutrinos and is establishing the planetary Th/U ratio. Their 2016 results give a global Th/U value of 4, with uncertainties of +5 and -3, which is consistent with chondritic and planetary values. Both detectors continue to count. The SNO+ detector (Canada) has recently filled with liquid scintillation that permits it to start detecting geoneutrinos.

Future detectors will be in China and include JUNO and Jinping. The JUNO detector will begin counting in early 2020s, and the Jinping detector is likely to begin a few years later. A proposed ocean bottom detector can assess the mantle only contribution to the global radiogenic power. Moreover, an ocean bottom detector can be used to map the geographical extent and assess the radiogenic power of structures in the deep interior (e.g., LLSVP and Transition Zone stagnant slabs (e.g., megaliths, second continents)).

3 detectors (KamLAND, JUNO, Jinping), laterally separated by a mantle depth, will see the same mantle and provide a critical test of models invoking a "second continent" that is gravitationally stabilized at the base of the Transition Zone and feeding magmatism along eastern China continental region.