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

Oct 2022

Neutrino oscillation experiments have measured precisely the mass-squareddifferences ($\Delta m^2_{21}$, $\Delta m^2_{31}$) of three neutrino masseigenstates, and the leptonic mixing angles ($\theta_{12},~ \theta_{13},~\theta_{23}$) by utilizing both neutrino and anti-neutrino oscillations. Thepossible CPT violation may manifest itself in the difference of neutrino andanti-neutrino oscillation parameters, making these experiments promising toolsfor testing CPT invariance. We investigate empirically the sensitivity of theCPT test via the difference in mass-squared splittings$\delta_{\nu\overline{\nu}}(\Delta m^2_{31})$ and in leptonic mixing angles$\delta_{\nu\overline{\nu}}(\sin^2\theta_{23})$ with the synergy of T2K-II,NO$\nu$A extension, and JUNO experiments. If the CPT symmetry is found to beconserved, the joint analysis of the three experiments will be able toestablish limits of $\delta_{\nu\overline{\nu}}(\Delta m^2_{31})<5.3\times10^{-3} \text{eV}^2$ and $\delta_{\nu\overline{\nu}}(\sin^2\theta_{23})<0.10$at 3$\sigma$ C. L. on the possible CPT violation. We find that with$\delta_{\nu\overline{\nu}}(\Delta m^2_{31})$, the dependence of thestatistical significance on the relevant parameters to exclude the CPTconservation is marginal, and that, if the difference in the best-fit values of$\Delta m^2_{31}$ and $\Delta \overline{m}^2_{31}$ measured by MINOS(+) andNO$\nu$A persists as the true, the combined analysis will rule out the CPTconservation at 4$\sigma$ C. L.. With the$\delta_{\nu\overline{\nu}}(\sin^2\theta_{23})$, the statistical significanceto 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 moreif the difference in the best-fit values of $\theta_{23}$ and$\overline{\theta}_{23}$ remains as the true.

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