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.
Highlights
Many solar, atmospheric, reactor, and accelerator neutrino experiments have firmly established the existence of neutrino oscillations
We restrict our study to four different scenarios that could take place in the presence of physics beyond the standard model
We have presented the sensitivity to the determination of the θ23 octant (θ23 ≤ π/4 or θ23 ≥ π/4) in Deep Underground Neutrino Experiment (DUNE) in four different scenarios
Summary
Atmospheric, reactor, and accelerator neutrino experiments have firmly established the existence of neutrino oscillations. Neutrino oscillations can be parametrized in terms of six physical variables, namely by three mixing angles θ12, θ23, and θ13, a phase δCP, and two squared-mass differences Δm221 1⁄4 m22 − m21 and Δm231 1⁄4 m23 − m21. These parameters are experimentally quite precisely determined, with the exception of the CP phase δCP. As to the mixing angle θ23, one still do not know in which octant it lies (θ23 < 45° or θ23 > 45°). As to the mixing angle θ23, known as the atmospheric angle, the fits on global data indicate that θ23 The order of the masses of three light neutrinos (ν1, ν2, ν3) remains unknown, namely whether it is m3 ≥ m1; m2 (normal hierarchy, NH) or m3 ≤ m1; m2 (inverted hierarchy, IH).
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