Non-standard interactions and the CP phase measurements in neutrino oscillations at low energies

We study the effects of non-standard interactions (NSI) and the genuine CP phase δ_D in neutrino oscillations at low, E_ν≲1 GeV, and very low, E_ν≲0.1 GeV, energies. For experimental setup with baseline and neutrino energy tuned to the first 1-3 oscillation maximum, we develop a simple analytic formalism to show the effects of NSI. The vacuum mimicking and its violation as well as the use of the separation basis play a central role in our formalism. The NSI corrections that affect the CP phase measurement mainly come from the violation of vacuum mimicking as well as from the corrections to the 1-3 mixing angle and mass-squared difference. We find that the total NSI correction to the ν_μ−ν_e probability P_μe can reach 20%−30% (1σ) at T2(H)K. Correspondingly, the correction to the CP phase can be as large as 50^∘ and hence significantly deteriorates the CP sensitivity at T2(H)K. The proposed TNT2K experiment, a combination of T2(H)K and the short baseline experiment μKam that uses the Super-K/Hyper-K detector at Kamioka to measure the oscillation of the antineutrinos from muon decay at rest (μDAR), can substantially reduce the degeneracy between NSI and the genuine CP phase δ_D to provide high CP sensitivity. The NSI correction to P_μe is only 2% (1σ) for μDAR neutrinos.