Searching for non-unitary neutrino oscillations in the present T2K and NO ν A data

Abstract

The mixing of three active neutrino flavors is parameterized by the unitary PMNS matrix. If there are more than three neutrino flavors and if the extra generations are heavy iso-singlets, the effective 3 × 3 mixing matrix for the three active neutrinos will be non-unitary. We have analyzed the latest T2K and NOνA data with the hypothesis of non-unitary mixing of the active neutrinos. We found that the 2019 NOνA data slightly (at ∼1σ CL) prefer the non-unitary mixing over unitary mixing. In fact, allowing the non-unitary mixing brings the NOνA best-fit point in the sin 2θ23- δCP plane closer to the T2K best-fit point. The 2019 T2K data, on the other hand, cannot rule out any of the two mixing schemes. A combined analysis of the NOνA and T2K 2019 data prefers the non-unitary mixing at 1σ CL. We derive constraints on the non-unitary mixing parameters using the best-fit to the combined NOνA and T2K data. These constraints are weaker than previously found. The latest 2020 data from both the experiments prefer non-unitarity over unitary mixing at 1σ CL. The combined analysis prefers non-unitarity at 2σ CL. The stronger tension, which exists between the latest 2020 data of the two experiments, also gets reduced with non-unitary analysis.