Updated bounds on the (1,2) neutrino oscillation parameters after first JUNO results

TL;DR

This work updates the global three-neutrino oscillation analysis for the leading $(\nu_1,\nu_2)$ parameters $(\delta m^2,\,\sin^2\theta_{12})$ after incorporating 2025 SNO$^+$ and JUNO results. It implements an external-constraint approach by adding the two-parameter $\chi^2$ maps from SNO$^+$ and JUNO to the rest-of-the-world (RoW) data and marginalizing subleading parameters, yielding refined bounds. The combined fit yields $\delta m^2 = (7.48 \pm 0.10) \times 10^{-5}\,{ m eV}^2$ and $\sin^2\theta_{12} = 0.3085 \pm 0.0073$ with a correlation $\rho = -0.20$, with JUNO providing the dominant precision improvement. Mass-ordering effects remain at the permill level but could become relevant with future high-precision JUNO data; overall, the results are consistent across datasets and tighten the predictions for solar- and reactor-neutrino oscillations within the $3\nu$ framework.

Abstract

Within the standard $3ν$ framework, we discuss updated bounds on the leading oscillation parameters related to the $(ν_1,\,ν_2)$ states, namely, the squared mass difference $δm^2=m^2_2-m^2_1$ and the mixing parameter $\sin^2θ_{12}$. A previous global analysis of 2024 oscillation data estimated $δm^2$ and $\sin^2θ_{12}$ with fractional $1σ$ errors of about $2.3\%$ and $4.5\%$, respectively. First we update the analysis by applying the latest SNO+ constraints, that slightly shift the $(δm^2,\,\sin^2θ_{12})$ best fits. Then we apply the constraints placed by the first JUNO results, that significantly reduce the uncertainties of both parameters. Our updated global bounds (as of 2025) can be summarized as: $δm^2/10^{-5}{\rm eV}^2 = 7.48\pm 0.10$ and $\sin^2θ_{12}=0.3085\pm0.0073$ (with correlation $ρ=-0.20$), corresponding to $1σ$ uncertainties as small as $1.3\%$ and $2.4\%$, respectively. We also comment on minor physical and statistical effects that, in the future, may contribute to lift the current mass-ordering degeneracy of $(δm^2,\,θ_{12})$ estimates.

Figures (3)

• Figure 1: Bounds at $N_\sigma$ standard deviations for $\delta m^2$ (upper panels) and $\sin^2\theta_{12}$ (lower panels) for NO (blue curves) e IO (red curves) as obtained from a global data analysis of 2024 oscillation data Capozzi:2025wyn (left panels), including---as detailed in this work---the latest 2025 SNO+ data SNO:2025chx (middle panels), plus the first 2025 JUNO data JUNO:2025gmd (right panels). The overall offset between the IO and NO curves is unchanged from Capozzi:2025wyn. See the text for details.
• Figure 2: Regions allowed at $N_\sigma=2$ ($\Delta\chi^2=4$) by separate and combined constraints in the plane $(\delta m^2,\,\sin^2\theta_{12})$, distinguished by different colors. The same colors are used to mark the corresponding best-fit points (dots).
• Figure 3: Global $3\nu$ oscillation analysis (2025): Current $2\sigma$ bounds on the mass parameters $(\Delta m^2_{ee},\,\delta m^2)$ that govern the JUNO oscillation frequencies, for both NO (blue) and IO (red). The global $\Delta\chi^2$ offset between IO and NO is also reported.