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

Abstract

We study the effects of non-standard interactions (NSI) and the genuine CP phase δD in neutrino oscillations at low, Ev ≲ 1 GeV, and very low, Ev ≲ 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 νμ − νe probability Pμe 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 δD to provide high CP sensitivity. The NSI correction to Pμe is only 2% (1σ) for μDAR neutrinos.