A hybrid setup for fundamental unknowns in neutrino oscillations using T2HK ($ν$) and $μ$-DAR ($\barν$)

Abstract

Neutrino mass hierarchy, CP-violation, and octant of $θ_{23}$ 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 ($\barν$) in conjunction with full exposure from T2K and NO$ν$A can resolve the issue of mass hierarchy at greater than 3$σ$ C.L. irrespective of the choices of hierarchy, $δ_{\mathrm{CP}}$, and $θ_{23}$. This hybrid setup can also establish the CP-violation at 5$σ$ C.L. for $\sim$ 55% choices of $δ_{\mathrm{CP}}$, whereas the same for conventional T2HK ($ν+ \barν$) setup along with T2K and NO$ν$A is around 30%. As far as the octant of $θ_{23}$ is concerned, this hybrid setup can exclude the wrong octant at 5$σ$ C.L. if $θ_{23}$ is at least $3^{\circ}$ away from maximal mixing for any $δ_{\mathrm{CP}}$.

18 pages, 28 pdf figures, 1 table. Minor changes in the text. A new footnote added. Accepted in JHEP