Parameter Degeneracy and Reactor Experiments

Degeneracies of the neutrino oscillation parameters are explained using the sin² 2θ ₁₃ - s₂₃² plane. Measurements of sin² 2θ₁₃ by reactor experiments are free from the parameter degeneracies which occur in accelerator appearance experiments, and reactor experiments play a role complementary to accelerator experiments. It is shown that the reactor measurement may be able to resolve the degeneracy in θ₂₃ if sin² 2θ₁₃ and cos² 2θ₂₃ are relatively large.