Prospects for Measurement of the Neutrino Mass Hierarchy

Abstract

The unknown neutrino mass hierarchy—whether the ν3 mass eigenstate is the heaviest or the lightest—represents a major gap in our knowledge of neutrino properties. Determining the hierarchy is a critical step toward further precision measurements in the neutrino sector. The hierarchy is also central to interpreting the next generation of neutrinoless double-β decay results, plays a role in numerous cosmological and astrophysical questions, and serves as a powerful model discriminant for theories of neutrino mass generation and unification. Various current and planned experiments claim sensitivity for establishing the neutrino mass hierarchy. I review the most promising of these here, paying special attention to points of concern and consolidating the projected sensitivities into an outlook for the years ahead.