Solar Neutrino Results and Future Opportunities with Borexino

Borexino started operations in 2007 with background conditions that were low enough for measurements of ⁷Be neutrinos, ⁸B neutrinos with low threshold energy, pep neutrinos, and a new upper limit on CNO neutrinos. These data provided the first direct probe of neutrino oscillations in the energy range covering the MSW transition from vacuum oscillations to matter-effect oscillations. Lower backgrounds will improve the accuracy of current measurements and provide an opportunity for possible measurement of pp and CNO neutrinos. The first effort to reduce background by scintillator re-purification using water extraction started in 2010 with a successful campaign that lowered ⁸⁵Kr and ²¹⁰Bi backgrounds. Data for a possible measurement of pp neutrinos are being analyzed. Recent improvements in scintillator re-purification have been identified that could reduce backgrounds to yet lower levels for a possible measurement of CNO neutrinos. The current results, the scintillator purification methods, and the future scientific opportunities for solar neutrino research will be discussed.