Measuring the Leptonic CP Phase in Neutrino Oscillations with Non-Unitary Mixing

Abstract

Non-unitary neutrino mixing implies an extra CP violating phase that can fake the leptonic Dirac CP phase δ CP of the simplest three-neutrino mixing benchmark scheme. This would hinder the possibility of probing for CP violation in accelerator-type experiments. We take T2K and T2HK as examples to demonstrate the degeneracy between the "standard" (or "non-unitary") and "nonunitary" CP phases. We find, under the assumption of non-unitary mixing, that their CP sensitivities severely deteriorate. Fortunately, the Tokai'N Toyama to Kamioka (TNT2K) proposal of supplementing T2(H)K with a µDAR source for better measurement of δ CP can partially break the CP degeneracy by probing both cos δ CP and sin δ CP dependences in the wide spectrum of the µDAR flux. We also show that the further addition of a near detector to the µDAR setup can eliminate the degeneracy completely. This summary is based on ref [1].