An astonishing culmination of discoveries taking place over the last decade has led to a revolution in our understanding of neutrinos–one of nature’s most elusive particles. Whereas just ten years ago it was commonly accepted that neutrinos were massless particles, a number of key experiments have shown that concept was incorrect. Experiments studying neutrinos from atmospheric, solar, and reactor sources have shown conclusively that neutrinos change flavor and, as a consequence, have a very small but finite mass. This serves to remind us that the standard model of nuclear and particle physics is incomplete. Knowledge of the neutrino mass can provide direction as how to extend that model.
