2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/182513Electron antineutrino interactions above the inverse beta decay energy of protons ($E_\barν_e>$1.8) where 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 $\barν_{e}$ flux, assumed having the $^8$B solar neutrino energy spectrum, of 1.1$\times10^{5}$ cm$^{-2}$~s$^{-1}$ (90% C.L.) was set with a 7.8 ton $\times$ year exposure. This upper limit corresponds to a solar neutrino transition probability, $ν_{e} \to \barν_{e}$, 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.10 pages, 9 figures, 5 tablesHigh Energy Physics - Experimenttext