A study of invisible neutrino decay at DUNE and its effects on θ 23 measurement

We study the consequences of invisible decay of neutrinos in the context of the DUNE experiment. We assume that the third mass eigenstate is unstable and decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector volume of 40 kt. We obtain the expected sensitivity on the rest-frame life-time τ ₃ normalized to the mass m ₃ as τ₃ /m ₃ > 4 .50 × 10^-11 s/eV at 90% C.L. for a normal hierarchical mass spectrum. We also find that DUNE can discover neutrino decay for τ₃ /m ₃ > 4 .27 × 10^-11 s/eV at 90% C.L. In addition, for an unstable ν₃ with an illustrative value of τ₃ /m ₃ = 1 .2 × 10^-11 s/eV, the no decay case could get disfavoured at the 3 σ C.L. At 90% C.L. the expected precision range for this true value is obtained as 1 .71 × 10^-11 > τ₃ /m ₃ > 9 .29 × 10^-12 in units of s/eV. We also study the correlation between a non-zero τ₃ /m ₃ and standard oscillation parameters and find an interesting correlation in the appearance and disappearance channels with the mixing angle θ ₂₃. This alters the octant sensitivity of DUNE, favorably (unfavorably) for true θ ₂₃ in the lower (higher) octant. The effect of a decaying neutrino does not alter the hierarchy or CP violation discovery sensitivity of DUNE in a discernible way.