Determine the neutrino mass ordering (normal vs inverted)

Determine whether the neutrino mass eigenstate ordering is normal (m1 < m2 < m3) or inverted (m3 < m1 < m2) by establishing the position of m3 relative to m1 and m2 using oscillation measurements of electron antineutrinos.

Background

In the three-flavor neutrino oscillation framework, flavor states are mixtures of mass eigenstates $\nu_1, \nu_2, \nu_3$ with splittings $\Delta m^2_{21}$ and $\Delta m^2_{31}$. While the ordering of $m_1$ and $m_2$ is established from solar neutrino data, the relative position of $m_3$ remains unresolved.

The JUNO experiment is designed to measure precise reactor antineutrino spectra at a 52.5 km baseline, where interference between solar- and atmospheric-scale oscillations imprints a fine spectral structure that is sensitive to the neutrino mass ordering. Resolving this unknown is a primary long-term goal of JUNO.