Back to (Mass-)Square(d) One: The Neutrino Mass Ordering in Light of Recent Data

TL;DR

Recent updates in neutrino oscillation data from T2K and NOvA experiments have diminished the previous strong preference for the normal neutrino mass ordering, impacting future research directions.

Contribution

This paper analyzes the latest neutrino oscillation data to reassess the neutrino mass ordering, showing the preference for normal ordering has significantly decreased.

Findings

Preference for normal ordering has vanished with new data.

Future experiments will be crucial for definitive determination.

Implications for neutrinoless double beta decay and cosmology.

Abstract

We inspect recently updated neutrino oscillation data -- specifically coming from the Tokai to Kamioka and NuMI Off-axis $\nu_e$ Appearance experiments -- and how they are analyzed to determine whether the neutrino mass ordering is normal ($m_1 < m_2 < m_3$) or inverted ($m_3 < m_1 < m_2$). We show that, despite previous results giving a strong preference for the normal ordering, with the newest data from T2K and NOvA, this preference has all but vanished. Additionally, we highlight the importance of this result for non-oscillation probes of neutrinos, including neutrinoless double beta decay and cosmology. Future experiments, including JUNO, DUNE, and T2HK will provide valuable information and determine the mass ordering at a high confidence level.