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Resolving θ23 degeneracy by accelerator and reactor neutrino oscillation experiments

Abstract:

If the lepton mixing angle θ23 is not maximal, there arises a problem of ambiguity in determining θ23 due to the existence of two degenerate solutions, one in the first and the other in the second octant. We discuss an experimental strategy for resolving the θ23 octant degeneracy by combining reactor measurement of θ13 with accelerator νμ disappearance and νe appearance experiments. The robustness of the θ23 degeneracy and the difficulty in lifting it only by accelerator experiments with conventional νμ (and ν̄μ) beams are demonstrated by analytical and numerical treatments. Our method offers a way to overcome the difficulty and can resolve the degeneracy between solutions sin 2θ23=0.4 and sin 2θ23=0.6 if sin 22θ13 0.05 at 95% CL by assuming the T2K phase II experiment and a reactor measurement with an exposure of 10 GW•kt•yr. The dependence of the resolving power of the octant degeneracy on the systematic errors of reactor experiments is also examined. © 2006 The American Physical Society.