Paper detail

Octant Degeneracy and Plots of Parameter Degeneracy in Neutrino Oscillations Revisited

The three kinds of parameter degeneracy in neutrino oscillation, the intrinsic, sign and octant degeneracy, form an eight-fold degeneracy. The nature of this eight-fold degeneracy can be visualized on the ($\sin^22θ_{13}$, $1/\sin^2θ_{23}$)-plane, through quadratic curves defined by $P(ν_μ\toν_e)=$ const. and $P(\barν_μ\to\barν_e)=$ const., along with a straight line $P(ν_μ\toν_μ)=$ const. After $θ_{13}$ was determined by reactor neutrino experiments, the intrinsic degeneracy in $θ_{13}$ transforms into an alternative octant degeneracy in $θ_{23}$, which can potentially be resolved by incorporating the value of $P(ν_μ\toν_μ)$. In this paper, we analytically discuss whether this octant parameter degeneracy is resolved or persists in the future long baseline accelerator neutrino experiments, such as T2HK, DUNE, T2HKK and ESS$ν$SB. It is found that the energy spectra near the first oscillation maximum are effective in resolving the octant degeneracy, whereas those near the second oscillation maximum are not.