Stringent constraint on CPT violation with the synergy of T2K-II, NO$\nu$A extension, and JUNO

Abstract

Neutrino oscillation experiments have measured precisely the mass-squared differences of three neutrino mass eigenstates, and three leptonic mixing angles by utilizing both neutrino and anti-neutrino oscillations. The possible CPT violation may manifest itself in the difference of neutrino and anti-neutrino oscillation parameters, making these experiments promising tools for testing CPT invariance. We investigate empirically the sensitivity of the CPT test via the difference in mass-squared splittings ($\Delta m_{31}^2-\Delta {\overline{m}}_{31}^2$) and in leptonic mixing angles (${\sin }^2{\theta }_{23}-{\sin }^2{\overline{\theta }}_{23}$) with the synergy of T2K-II, NO$\nu$A extension, and JUNO experiments. If the CPT symmetry is found to be conserved, the joint analysis of the three experiments will be able to establish limits of $|\Delta m_{31}^2-\Delta {\overline{m}}_{31}^2|$ < $5.3\times 10^{-3}{\text{eV}}^2$ and $|{\sin }^2{\theta }_{23}-{\sin }^2{\overline{\theta }}_{23}|$ < $0.10$ at 3$\sigma$ C. L. on the possible CPT violation. We find that with ($\Delta m_{31}^2-\Delta {\overline{m}}_{31}^2$), the dependence of the statistical significance on the relevant parameters to exclude the CPT conservation is marginal, and that, if the difference in the best-fit values of $\Delta m_{31}^2$ and $\Delta {\overline{m}}_{31}^2$ measured by MINOS(+) and NO$\nu$A persists as the true, the combined analysis will rule out the CPT conservation at 4$\sigma$ C. L.. With the (${\sin }^2{\theta }_{23}-{\sin }^2{\overline{\theta }}_{23}$), the statistical significance to exclude CPT invariance depends strongly on the true value of ${\theta }_{23}({\overline{\theta }}_{23})$. In case of maximal mixing of ${\theta }_{23}$, the CPT conservation will be excluded at 3$\sigma$ C. L. or more if the difference in the best-fit values of ${\theta }_{23}$ and ${\overline{\theta }}_{23}$ remains as the true.

10 pages, 10 figures

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