One of the major open problems of neutrino physics is mass ordering (MO). We discuss the prospects of measuring MO with two under-construction experiments T2HK and JUNO. JUNO alone is expected to measure MO with greater than $3\sigma$ significance as long as certain experimental challenges are met. In particular, JUNO needs better than 3% energy resolution for MO measurement. On the other hand, T2HK has rather poor prospects at measuring the MO, especially for certain ranges of the $CP$ violating parameter ${\delta }_{CP}$, posing a major drawback for T2HK. In this article we show that the synergy between JUNO and T2HK will bring twofold advantage. First, the synergy between the two experiments helps us determine the MO at a very high significance. With the baseline setup of the two experiments, we have a greater than $9\sigma$ determination of the MO for all values of ${\delta }_{CP}$. Second, the synergy also allows us to relax the constraints on the two experiments. We show that JUNO could perform extremely well even for an energy resolution of 5%, while for T2HK the MO problem with “bad” values of ${\delta }_{CP}$ goes away. The MO sensitivity for the combined analysis is expected to be greater than $6\sigma$ for all values of ${\delta }_{CP}$ and with just 5% energy resolution for JUNO.

• Received 18 July 2022
• Accepted 17 November 2022

DOI:https://doi.org/10.1103/PhysRevD.106.115013

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society