Neutrino versus antineutrino oscillation parameters at DUNE and Hyper-Kamiokande experiments

Testing, in a nontrivial, model-independent way, the hypothesis that the three-massive-neutrinos paradigm properly describes nature is among the main goals of the current and the next generation of neutrino oscillation experiments. In the coming decade, the DUNE and Hyper-Kamiokande experiments will be able to study the oscillation of both neutrinos and antineutrinos with unprecedented precision. We explore the ability of these experiments, and combinations of them, to determine whether the parameters that govern these oscillations are the same for neutrinos and antineutrinos, as prescribed by the $CPT$-theorem. We find that both DUNE and Hyper-Kamiokande will be sensitive to unexplored levels of leptonic $CPT$-violation. Assuming the parameters for neutrino and antineutrino oscillations are unrelated, we discuss the ability of these experiments to determine the neutrino and antineutrino mass-hierarchies, atmospheric-mixing octants, and $CP$-odd phases, three key milestones of the experimental neutrino physics program. Additionally, if the $CPT$-symmetry is violated in nature in a way that is consistent with all present neutrino and antineutrino oscillation data, we find that DUNE and Hyper-Kamiokande have the potential to ultimately establish leptonic $CPT$-invariance violation.

Figure 1

Allowed regions of parameter space at 99% credibility assuming the true values of parameters in Table 1 with ${\sin }^2{\theta }_{23}=0.441$. Parameters are projected down to common axes for comparison. The red contours display the regions allowed for the neutrino parameters, and blue contours display the regions allowed for antineutrino parameters (bars on parameters omitted). We also include the results of a $CPT$-conserving analysis in black. The dashed regions display the additional parameter space allowed at 99% credibility when the analysis is repeated without the prior on ${\sin }^2(2{\overline{\theta }}_{13})$ from the Daya Bay experiment, Eq. (2.3).

Figure 2

Identical to Fig. 1; however, here the true value of ${\sin }^2{\theta }_{23}$ is 0.500.

Figure 3

Sensitivity to $CPT$ violation at various combinations of experiments. Each row displays sensitivity to $\mathrm{\Delta }({\sin }^2{\theta }_{13})$ (left), $\mathrm{\Delta }(\mathrm{\Delta }{m}_{31}^2)$ (center), and $\mathrm{\Delta }({\delta }_{CP})$ (right) at 68.3% (blue), 95% (orange), and 99% (red) credibility. Here, “HK B” represents the Hyper-Kamiokande beam-based events, and “HK AB” represents the combination of beam- and atmospheric-based events. In this figure, the prior information on ${\sin }^2(2{\overline{\theta }}_{13})$ from the Daya Bay experiment is included.

Figure 4

Identical to Fig. 3, however, in this figure, the prior information on ${\sin }^2(2{\overline{\theta }}_{13})$ from the Daya Bay experiment is not included.

Figure 5

Results of the measurement of the parameters ${\delta }_{CP}$ and ${\overline{\delta }}_{CP}$ in the $CPT$-violating Scenario A, in which the values of these two parameters are maximally different. Each panel represents the measurement from a particular combination of experiments, with all ten unseen parameters marginalized. Shown are the 95% (orange), and 99% (red) credible regions for the two parameters. Solid lines display the results for the analysis including the prior on ${\sin }^2(2{\overline{\theta }}_{13})$ from the Daya Bay experiment, and dotted lines display results without this prior.

Figure 6

Results of the measurement of the parameters ${\sin }^2{\theta }_{13}$ and ${\sin }^2{\overline{\theta }}_{13}$ in the $CPT$-violating Scenario B. Each panel represents the measurement from a particular combination of experiments, with all ten unseen parameters marginalized. Shown are the 95% (orange), and 99% (red) credible regions for the two parameters. Solid lines display the results for the analysis including the prior on ${\sin }^2(2{\overline{\theta }}_{13})$ from the Daya Bay experiment, and dotted lines display results without this prior.