Parameter degeneracy and reactor experiments

Degeneracies of the neutrino oscillation parameters are explained using the ${\sin }^{2}2{\theta }_{13}$–$s_{23}^2$ plane. Measurements of ${\sin }^{2}2{\theta }_{13}$ 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 ${\theta }_{23}$ if ${\sin }^{2}2{\theta }_{13}$ and ${\cos }^{2}2{\theta }_{23}$ are relatively large.