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

TL;DR

This paper evaluates how long-baseline neutrino experiments at J-PARC can test the unitarity of neutrino mixing, providing bounds on non-unitary parameters and demonstrating T2HK's superior sensitivity.

Contribution

It introduces a detailed analysis of the sensitivity of T2HK, T2HKK, and T2K experiments to non-unitary neutrino mixing parameters, highlighting T2HK's enhanced capabilities.

Findings

T2HK can establish unitarity at above 2σ C.L. for NU parameter ~10^{-2}.

Bounds on NU parameter α_{21} are 0.028 (T2K), 0.0026 (T2HKK), 0.005 (T2HK).

T2HK has superior sensitivity limit on NU parameter compared to T2HKK and T2K.

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.