Prospects for Measurement of the Neutrino Mass Hierarchy

TL;DR

Determining the neutrino mass hierarchy is crucial for understanding neutrino properties, impacting cosmology, particle physics, and future experiments, with several promising experiments aiming to resolve this fundamental question.

Contribution

This paper reviews current and planned experiments targeting the neutrino mass hierarchy, analyzing their sensitivities and challenges to guide future research.

Findings

Multiple experiments have potential sensitivity to the hierarchy.

Projected sensitivities vary and depend on experimental design.

Resolving the hierarchy will significantly impact neutrino physics and cosmology.

Abstract

The unknown neutrino mass hierarchy -- whether the $\nu_3$ 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 beta 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. We 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.