Physics potential of the combined sensitivity of T2K-II, $\mathrm{NO}\nu \mathrm{A}$ extension, and JUNO

Leptonic CP violation search, neutrino mass hierarchy determination, and the precision measurements of oscillation parameters for a unitary test of the leptonic mixing matrix are among the major targets of the ongoing and future neutrino oscillation experiments. The work explores the physics reach for these targets by around 2027, when the third generation of the neutrino experiments starts operation, with a combined sensitivity of three experiments: T2K-II, $\mathrm{NO}\nu \mathrm{A}$ extension, and JUNO. It is shown that a joint analysis of these three experiments can conclusively determine the neutrino mass hierarchy. Also, at certain values of true ${\delta }_{CP}$, it provides closely around a $5\sigma$ confidence level (C.L.) to exclude $CP$-conserving values and more than a 50% fractional region of true ${\delta }_{CP}$ values can be explored with a statistic significance of at least a $3\sigma$ C.L. Besides, the joint analysis can provide unprecedented precision measurements of the atmospheric neutrino oscillation parameters and a great offer to solve the ${\theta }_{23}$ octant degeneracy in the case of nonmaximal mixing.

Figure 1

Expected event spectra of the signal and background as a function of reconstructed neutrino energy for T2K-II. The top (bottom) spectra are for the appearance (disappearance) samples and the left (right) spectra are for $\nu$-mode ($\overline{\nu }$-mode). The same oscillation parameters as in Ref. [33] are used.

Figure 2

Expected event spectra of the signal and background as a function of reconstructed neutrino energy for $\mathrm{NO}\nu \mathrm{A}\text{−}\mathrm{II}$. The top (bottom) spectrum is for the appearance (disappearance) channel and the left (right) spectrum is for $\nu$-mode ($\overline{\nu }$-mode). Normal MH, ${\delta }_{CP}=0$, and other oscillation parameters given in Table 1 are assumed.

Figure 3

JUNO event rate calculated at the same oscillation parameters as Ref. [26].

Figure 4

MH sensitivities as a function of true ${\delta }_{CP}$ calculated for various experimental setups (top plot); for all considered experiments but at different ${\sin }^2{\theta }_{23}$ values (center plot); and for comparing two possible MH hypotheses (bottom plot). For the top and bottom plots, ${\sin }^2{\theta }_{23}=0.5$ is assumed to be true.

Figure 5

CPV sensitivity as a function of the true value of ${\delta }_{CP}$ obtained with different analyses. Normal MH and ${\sin }^2{\theta }_{23}=0.5$ are assumed to be true. The top (bottom) plot is with the MH assumed to be unknown (known) in the analysis, respectively.

Figure 6

CPV sensitivity as a function of the true value of ${\delta }_{CP}$ obtained with a joint analysis of all considered experiments at different true ${\sin }^2{\theta }_{23}$ values (0.43, 0.5, 0.6). The top (bottom) plot is with the normal (inverted) MH, respectively, and assumed to be true. The MH is assumed to be unknown in the analysis.

Figure 7

(a) Allowed region of ${\sin }^2{\theta }_{13}-{\delta }_{CP}$ at a $3\sigma$ C.L. compared with a joint analysis of T2K-II and $\mathrm{NO}\nu \mathrm{A}\text{−}\mathrm{II}$ and the present constraint from the global data [7]. (b) Allowed region in the ${\sin }^2{\theta }_{23}-\mathrm{\Delta }{m}_{31}^2$ space at a 90% C.L. with various experimental setups. Normal MH and ${\sin }^2{\theta }_{23}=0.5$ are assumed to be true.

Figure 8

Allowed region of ${\sin }^2{\theta }_{23}$ at a $3\sigma$ C.L (a) and the statistical significance of excluding the wrong octant as a function of ${\sin }^2{\theta }_{23}$ (b). Normal MH and ${\delta }_{CP}=-\frac{\pi }{2}$ are assumed to be true.

Figure 9

Dependence of the neutrino MH sensitivity on the ${\theta }_{13}$ true values: ${\sin }^2{\theta }_{13}=0.02241$ is the best fit obtained with NuFIT 4.1 [7], ${\sin }^2{\theta }_{13}=0.02221$ is with NuFIT 5.0 [8], and ${\sin }^2{\theta }_{13}=0.02034$ is a $3\sigma$ C.L. lower limit. Normal MH and ${\sin }^2{\theta }_{23}=0.5$ are assumed to be true.

Figure 10

Dependence of the combined sensitivity on T2K-II POT exposure. (a) MH sensitivities as a function of true ${\delta }_{CP}$. (b) CPV sensitivity as a function of the true value of ${\delta }_{CP}$ obtained with a joint analysis of all considered experiments. Normal MH and ${\sin }^2{\theta }_{23}=0.5$ are assumed to be true.