# Resolving the octant of *θ* _{23} with T2K and NO*ν*A

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## Abstract

Preliminary results of MINOS experiment indicate that *θ* _{23} is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for *θ* _{23}: one in the lower octant (LO: *θ* _{23} < 45^{◦}) and the other in the higher octant (HO: *θ* _{23} > 45^{◦}). *ν* _{ μ } *→ ν* _{ e } oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NO*ν*A experiments. Because of the hierarchy-*δ* _{CP} degeneracy and the octant-*δ* _{CP} degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of *δ* _{CP} for which octant resolution is easy (challenging). However, for octant resolution the unfavorable *δ* _{CP} values of the neutrino data are favorable for the anti-neutrino data and vice-verse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NO*ν*A to resolve the octant ambiguity. If sin^{2} *θ* _{23} = 0.41, then NO*ν*A can rule out all the values of *θ* _{23} in HO at 2*σ* C.L., irrespective of the hierarchy and *δ* _{CP}. Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and anti-neutrino runs of 2.5 years each, a 2*σ* resolution of the octant becomes possible provided sin^{2} *θ* _{23} ≤ 0.43 or ≥ 0.58 for any value of *δ* _{CP}.

## Keywords

Neutrino Physics CP violation Beyond Standard Model## References

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