A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK (\u03bd) and \u03bc-DAR left(overline{nu}right)

Abstract

Neutrino mass hierarchy, CP-violation, and octant of θ23 are the fundamental unknowns in neutrino oscillations. In order to address all these three unknowns, we study the physics reach of a setup, where we replace the antineutrino run of T2HK with antineutrinos from muon decay at rest (μ-DAR). This approach has the advantages of having higher statistics in both neutrino and antineutrino modes, and lower beam-on backgrounds for antineutrino run with reduced systematics. We find that a hybrid setup consisting of T2HK (ν) and μ-DAR left(overline{nu}right) in conjunction with full exposure from T2K and NOνA can resolve the issue of mass hierarchy at greater than 3σ C.L. irrespective of the choices of hierarchy, δCP, and θ23. This hybrid setup can also establish the CP-violation at 5σ C.L. for ∼ 55% choices of δCP, whereas the same for conventional T2HK left(nu + overline{nu}right) setup along with T2K and NOνA is around 30%. As far as the octant of θ23 is concerned, this hybrid setup can exclude the wrong octant at 5σ C.L. if θ23 is at least 3° away from maximal mixing for any δCP.