Borexino: low energy solar neutrino spectroscopy

Borexino is a liquid scintillation detector with about 100 t fiducial volume, being developed for operation at Gran Sasso, Italy. Its mission is solar neutrino spectrscopy with signal and event thresholds above 0.35 MeV. The strongest signal in the detector will arise from 7Be neutrinos at the rate of about 50/day (in the standard solar model) via neutrino-electron scattering. High energy neutrinos such as 8B will also yield useful information. In addition, antineutrinos can be detected with high sensitivity. Borexino will be uniquely placed to tackle physics questions needing real-time low-energy sensitivity and high signal rates (inaccessible to present or planned experiments) such as: magnitudes and short-term variations (day/night, seasonal) of the 7Be neutrino flux, neutrino-electron scattering cross-sections at sub-MeV energies, and strong limits on antineutrinos from the sun. Answers from Borexino on these topics will have specific and critical implications for neutrino mass/mixing and magnetic moments