Search for electron antineutrino interactions with the Borexino Counting Test Facility at Gran Sasso.

Electron antineutrino interactions above the inverse beta decay energy of protons (E_ν̄e>1.8 MeV) 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 ν̄_e flux, assumed having the ⁸B solar neutrino energy spectrum, of 1.1×10⁵ cm^-2 s^-1 (90% C.L.) was set with a 7.8 ton × year exposure. This upper limit corresponds to a solar neutrino transition probability, ν_e→ν̄_e, 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. [ABSTRACT FROM AUTHOR]