Enhancing the sensitivity to neutrino oscillation parameters using synergy between T2K, NO$\nu$A and JUNO

TL;DR

Combining data from NO$ u$A, T2K, and JUNO significantly improves the determination of neutrino mass hierarchy and CP phase, resolving degeneracies and tensions present in current measurements through synergistic analysis.

Contribution

This study demonstrates how JUNO's precise measurements enhance the global neutrino oscillation analysis, resolving existing degeneracies and tensions in hierarchy and CP phase determination.

Findings

JUNO data can lift hierarchy--$ m extbf{ extit{δ}}_{ m CP}$ degeneracy.

JUNO improves constraints on $ extbf{ extit{sin}}^2 heta_{23}$ and $ extbf{ extit{δ}}_{ m CP}$ for NH.

JUNO's measurements resolve tensions between NO$ u$A and T2K for IH.

Abstract

We study the impact of combining the present NO$\nu$A and T2K data with simulated data from the JUNO experiment on the determination of the leptonic CP phase and the neutrino mass hierarchy. The current NO$\nu$A data exhibit a hierarchy--$\delta_{\rm CP}$ degeneracy, admitting both normal hierarchy (NH) with $\delta_{\rm CP} \in [0,180^\circ]$, and inverted hierarchy (IH) with $\delta_{\rm CP} \in [180^\circ,360^\circ]$ solutions at comparable significance, while T2K prefers $\delta_{\rm CP}\simeq 270^\circ$ for both hierarchies, leading to a $2\sigma$ tension between the two experiments for normal hierarchy. Using detailed GLoBES simulations, we show that future JUNO data with excellent hierarchy sensitivity, can lift the hierarchy--$\delta_{\rm CP}$ degeneracy in NO$\nu$A and strengthen the hierarchy reach of T2K in spite of having no $\delta_{\rm CP}$ sensitivity. Allowing the hierarchy to be a free parameter in the fit, if the true ordering is IH, JUNO aligns the NO$\nu$A and T2K allowed regions and resolves their present tension; if NH is true, the tension continues to persist. We also show that JUNO's precise measurement of $|\Delta_{31}|$ leads to improved constraints on $\sin^2\theta_{23}$ and $\delta_{\rm CP}$ for normal mass hierarchy in NO$\nu$A even though JUNO itself is insensitive to these parameters. Finally, updated solar parameter measurements from JUNO's first data release further enhance the combined precision. Our results demonstrate that JUNO plays a crucial synergistic role in the global neutrino oscillation programme, enabling a more robust determination of the mass ordering and improving the sensitivity to the CP phase when combined with long-baseline data.