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

Abstract

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

Comments: 17 pages, 5 figures