# Octant sensitivity for large *θ* _{13} in atmospheric and long-baseline neutrino experiments

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## Abstract

One of the unknown parameters in neutrino oscillation studies is the octant of the atmospheric neutrino mixing angle *θ* _{23}. In this paper, we discuss the possibility of determining the octant of *θ* _{23} in the long-baseline experiments T2K and NO*ν*A in conjunction with future atmospheric neutrino detectors, in the light of non-zero value of *θ* _{13} measured by reactor experiments. We consider two detector technologies for atmospheric neutrinos — magnetized iron calorimeter and non-magnetized Liquid Argon Time Projection Chamber. We present the octant sensitivity for T2K/NO*ν*A and atmospheric neutrino experiments separately as well as the combined sensitivity. For the long-baseline experiments, a precise measurement of *θ* _{13}, which can exclude degenerate solutions in the wrong octant, increases the sensitivity drastically. For *θ* _{23} = 39*°* and sin^{2} 2*θ* _{13} = 0.1, at least ~ 2*σ* sensitivity can be achieved by T2K + NO*ν*A for all values of *δ* _{CP} for both normal and inverted hierarchy. For atmospheric neutrinos, the moderately large value of *θ* _{13} measured in the reactor experiments is conducive to octant sensitivity because of enhanced matter effects. A magnetized iron detector can give a 2*σ* octant sensitivity for 500 kT yr exposure for *θ* _{23} = 39*°*, *δ* _{CP} = 0 and normal hierarchy. This increases to 3*σ* for both hierarchies by combining with T2K and NO*ν*A. This is due to a preference of different *θ* _{23} values at the minimum *χ* ^{2} by T2K/NO*ν*A and atmospheric neutrino experiments. A Liquid Argon type detector for atmospheric neutrinos with the same exposure can give higher octant sensitivity, due to the interplay of muon and electron contributions and superior resolutions. We obtain a ~ 3*σ* sensitivity for *θ* _{23} = 39*°* for normal hierarchy. This increases to ≿ 4*σ* for all values of *δ* _{CP} if combined with T2K/NO*ν*A. For inverted hierarchy the combined sensitivity is around 3*σ*.

## Keywords

Neutrino Physics CP violation## References

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