Discovery Potential of T2K and NOvA in the Presence of a Light Sterile Neutrino

TL;DR

This paper evaluates how the presence of a light sterile neutrino affects the ability of T2K and NOvA experiments to discover CP-violation and determine the neutrino mass hierarchy, revealing significant sensitivity deterioration.

Contribution

It introduces the bi-probability representation in the 4-flavor framework and assesses the experiments' discovery potential considering a light sterile neutrino.

Findings

Sensitivity to CP-violation is significantly reduced by sterile neutrinos.

The experiments' ability to determine the mass hierarchy is compromised.

Uncertainties in phase reconstruction are approximately 40° for delta13 and 50° for delta14.

Abstract

We study the impact of one light sterile neutrino on the prospective data expected to come from the two presently running long-baseline experiments T2K and NOvA when they will accumulate their full planned exposure. Introducing for the first time, the bi-probability representation in the 4-flavor framework, commonly used in the 3-flavor scenario, we present a detailed discussion of the behavior of the numu to nue and numubar to nuebar transition probabilities in the 3+1 scheme. We also perform a detailed sensitivity study of these two experiments (both in the stand-alone and combined modes) to assess their discovery reach in the presence of a light sterile neutrino. For realistic benchmark values of the mass-mixing parameters (as inferred from the existing global short-baseline fits), we find that the performance of both these experiments in claiming the discovery of the CP-violation induced by the standard CP-phase delta13 equivalent to delta, and the neutrino mass hierarchy get substantially deteriorated. The exact loss of sensitivity depends on the value of the unknown CP-phase delta14. Finally, we estimate the discovery potential of total CP-violation (i.e., induced simultaneously by the two CP-phases delta13 and delta14), and the capability of the two experiments of reconstructing the true values of such CP-phases. The typical (1 sigma level) uncertainties on the reconstructed phases are approximately 40 degree for delta13 and 50 degree for delta14.