Determination of the $θ_{23}$ octant in long baseline neutrino experiments within and beyond the standard model

Abstract

The recent data indicate that the neutrino mixing angle $θ_{23}$ deviates from the maximal-mixing value of 45$^\circ$, showing two nearly degenerate solutions, one in the lower octant (LO) ($θ_{23}<45^\circ$) and one in the higher octant (HO) ($θ_{23}>45^\circ$). We investigate, using numerical simulations, the prospects for determining the octant of $θ_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($θ_{23}-45^\circ$, $δ$)--plane, where $δ$ is the $CP$ phase, showing the true values of $θ_{23}$ for which the octant can be experimentally determined at 3$\,σ$, 2$\,σ$ and 1$\,σ$ confidence level. In particular, we study the impact of the possible nonunitarity of neutrino mixing on the experimental determination of $θ_{23}$ in those experiments.

17 pages, 5 figures