Atmospheric Mass-Squared Splitting at Sub-Percent Precision as a $CPT$ Symmetry Probe

TL;DR

This work tests CPT symmetry in the neutrino sector by comparing atmospheric mass-squared splittings, specifically $Δm^2_{31}$ and $Δ\overline{m}^2_{31}$, through the observable $\delta_{ν\overline{ν}}(Δm^2_{31})$. It develops a GLoBES-based framework that combines DUNE, Hyper-K, and JUNO to exploit complementary baselines, detection technologies, and disappearance channels, aiming for sub-$10^{-5}~\mathrm{eV}^2$ precision. The study finds that current data from T2K, NO$\nu$A, and Daya Bay show no CPT violation and that the next-generation synergy (Hyper-K with DUNE and/or JUNO) can reach sensitivities around $2\times 10^{-5}~\mathrm{eV}^2$ at 3$σ$, representing a ~60% improvement over earlier joint analyses. These results demonstrate the crucial role of multi-experiment coordination in probing fundamental spacetime symmetries with high precision.

Abstract

In this paper, we present an improved test of $CPT$ symmetry in the neutrino sector by analyzing the atmospheric mass-squared splittings, $Δm^2_{31}$ and $Δ\overline{m}^2_{31}$, using on-going JUNO and future DUNE and Hyper-Kamiokande experiments. Our study focuses on the discrepancy $δ_{ν\overlineν}(Δm^2_{31}) = Δm^2_{31} - Δ\overline{m}^2_{31}$, achieving unprecedented precision by exploiting the high statistics and reduced systematic uncertainties of these facilities. The combined analysis yields a sensitivity to $CPT$ violation at the level of $2\times 10^{-5}~\text{eV}^2$ at $3σ$ confidence level, representing a $60\%$ improvement over the joint T2K-NO$ν$A-JUNO analysis. These results highlight the crucial role of multi-experiment synergies in testing fundamental symmetries of nature.

Figures (5)

• Figure 1: Comparison of statistical configurations for $CPT$ sensitivity in DUNE (top) and Hyper-K (bottom). For DUNE, the 1:1 neutrino–antineutrino running configuration improves the $CPT$ sensitivity by approximately 4% compared to the 1:3 configuration, while for Hyper-K the corresponding improvement is about 2%.
• Figure 2: The current analyses from T2K t2kprd2023update (red) and NO$\nu$A nova20192d118E20POT (blue), along with their combined results incorporating Daya Bay dayabayprd2023 (green) data within 1$\sigma$ uncertainty, reveal no significant indication of $CPT$ violation in the atmospheric neutrino sector.
• Figure 3: The two-dimensional contours of $\Delta m^2_{31}$ and $\Delta \overline{m}^2_{31}$ at 3$\sigma$ C. L. constraints on the $CPT$ violation from current and future neutrino oscillation experiments (combined T2K+NO$\nu$A+JUNO, DUNE, Hyper-K, JUNO, and their combinations).
• Figure 4: Statistical significance to exclude $CPT$ conservation as a function of true$\delta_{\nu\overline{\nu}}(\Delta m^2_{31})$ under various experimental configurations.
• Figure 5: The bounds at 3$\sigma$ of $|\delta_{\nu\overline{\nu}}(\Delta m^2_{31})|$ to exclude $CPT$ conservation hypothesis across the 3$\sigma$ experimentally allowed range of $\sin^2\theta_{23} \in [0.40 - 0.62]$.