Searches for Geoantineutrino Flux from \({}^{{40}}\)K on the Basis of Data from the Borexino Detector

In addition to solar-neutrino fluxes, the Borexino detector is able to record antineutrino fluxes by employing reactions of elastic neutrino- and antineutrino-electron scattering. Antineutrino fluxes are produced within the Earth by natural-radioactivity isotopes and at the Earth’s surface by nuclear reactors of nuclear power plants. The most recent data accumulated by the Borexino detector are analyzed upon adding known antineutrino fluxes to the backgrounds and fluxes of solar neutrinos. This analysis made it possible to determine the flux of \({}^{40}\) K antineutrinos, which turned out to be quite significant in magnitude. At the same time, all fluxes of solar neutrinos are compatible with the low-metallicity model of the Sun.