Probing non-unitary neutrino mixing via long-baseline neutrino oscillation experiments based at J-PARC

Abstract

This paper investigates the capability of long-baseline experiments, which are making use of neutrinos that are coming from Japan Proton Accelerator Research Complex (J-PARC), in establishing the unitarity of active-neutrino mixing by ruling out the non-unitary mixing scheme as a function of true values of CP-violating phase $\delta_{\mathrm{CP}}$. It is found that T2HK can establish unitarity of active neutrino mixing at above 2$\sigma$ C.L. irrespective of neutrino mass hierarchy and true value of $\delta_{CP}$, if non-unitary (NU) parameter $\alpha_{21}$ is of the order of $10^{-2}$. Further, this paper is also discuss the bound on NU parameter in 21 sector and sensitivity limit of these experiments in determining NU parameter. It is found that the bounds on $\left(\alpha_{21}/2\right)$ are 0.028, 0.0026, 0.005 at 2$\sigma$ C.L. respectively for T2K, T2HK, and T2HKK. Moreover, it is also found that the sensitivity limit of T2HK on NU parameter is far better than that of both T2HKK and T2K.