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Abstract

Electron antineutrino interactions above the inverse beta decay energy of protons (E¯νe > 1.8MeV) were looked for with the Borexino counting test facility (CTF). One candidate event survived after rejection of background, which included muon-induced neutrons and random coincidences. An upper limit on the solar ¯νe flux, assumed having the 8B solar neutrino energy spectrum, of 1.1×105 cm−2s−1 (90% C.L.) was set with a 7.8 ton × year exposure. This upper limit corresponds to a solar neutrino transition probability, νe → ¯νe, of 0.02 (90% C.L.). Predictions for antineutrino detection with Borexino, including geoneutrinos, are discussed on the basis of background measurements performed with the CTF.