Prospects for the Mass Ordering (MO) and $θ_{23}$-Octant sensitivity in LBL experiments: UNO, DUNE \& NO$ν$A

Abstract: This article represents quantitative numerical analysis to find the sensitivity for the mass ordering and octant of atmospheric mixing angle $\theta_{23}$ within 3$\sigma$ range of oscillation parameters, in the context of three long base line (LBL) accelerator experiments viz. UNO, DUNE and NO$\nu$A. We notice that on the basis of quantitative sensitivity pertaining to the event rate, it is possible to investigate the mass ordering within all experiments. Conclusively, like NO$\nu$A and DUNE experiments, UNO experiment stands as better alternative for investigating mass ordering, especially when we need to cross check the results at higher beam energies and base line lengths. We observe that discrete solutions viz. {\it wrong octant-right $\delta_{CP}$, wrong octant-wrong $\delta_{CP}$} and {\it right octant-wrong $\delta_{CP}$} and continuous solutions arising due to submergence of discrete solutions with true solution are possible up to 3$\sigma$ level. It is UNO experiment that alone have the potential to remove these discrete solutions, while both NO$\nu$A and DUNE experiments have very poor tendency to remove these discrete solutions especially near the maximal mixing. We find that these discrete solutions can be resolved up to 3$\sigma$ level by the combined NO$\nu$A+DUNE+UNO data set, at all multiple degenerate solutions in the true parameter space considered under the study. Though replacing half the neutrino run with antineutrino run introduces qualitative advantage because of their different dependences on $\delta_{CP}$, but due to lower cross section and reduction in the statistics, addition of antineutrino data make the precision worse. Thus considering experimental data only in the neutrino mode, enhances $\delta_{CP}$ and $\theta_{23}$ precision significantly.