Neutrinos from the Sun: The 2003 Benjamin Franklin Medal in Physics presented to John Bahcall, Raymond Davis, Jr., and Masatoshi Koshiba

This award recognizes years of research by the laureates using elusive neutrinos to probe the internal workings of the sun. Bahcall and Davis identified an apparently fundamental problem: the fusion reactions that generate the sunʹs power deep in its core appeared to generate fewer neutrinos than expected. The number of neutrinos detected by Davis was only about a third the number calculated by Bahcall. Koshiba developed a new type of detector that not only confirmed the deficit but also showed that the neutrinos counted by Davis actually come from the Sun. Together the work of these three scientists prepared the way for the resolution of the puzzle, the discovery of a new property of neutrinos called “neutrino oscillations”. On the way from the sun, some neutrinos change identity and become nearly invisible in the detectors. This insight promises to open up new vistas in the fundamental physics of elementary particles.