pp-Solar Neutrino Spectroscopy: Return of the Indium Detector

A new indium-loaded liquid scintillator (LS) with up to 15wt% In and high light output promises a breakthrough in the 25y old proposal for observing pp solar neutrinos (nue) by tagged nue capture in 115In. Intense background from the natural beta-decay of In, the single obstacle blocking this project till now, can be reduced by more than x100 with the new In-LS. Only non-In background remains, dramatically relaxing design criteria. Eight tons of In yields ~400 pp nue/y after analysis cuts. With the lowest threshold yet, Q=118 keV, In is the most sensitive detector of the pp nue spectrum, the long sought touchstone for nue conversion.