A close look on 2-3 mixing angle with DUNE in light of current neutrino oscillation data

Abstract

Recent global fit analyses of oscillation data show a preference for normal mass ordering (NMO) at 2.5$\sigma$ and provide 1.6$\sigma$ indications for lower ${\theta }_{23}$ octant and leptonic CP violation. A high-precision measurement of ${\theta }_{23}$ is pivotal to convert these hints into discoveries. In this work, we study in detail the capabilities of DUNE to establish the deviation from maximal ${\theta }_{23}$ and to resolve its octant at high confidence levels. We exhibit the possible correlations and degeneracies among ${\sin }^2{\theta }_{23}$, $\Delta m_{31}^2$, and ${\delta }_{CP}$ in disappearance and appearance oscillation channels at the probability and event levels. Introducing for the first time, a bi-events plot in the plane of total $\nu$ and $\bar{\nu }$ disappearance events, we discuss the impact of ${\sin }^2{\theta }_{23}$ - $\Delta m_{31}^2$ degeneracy in establishing non-maximal ${\theta }_{23}$ and show how this degeneracy can be resolved by exploiting the spectral shape information in $\nu$ and $\bar{\nu }$ disappearance events. A 3$\sigma$ (5$\sigma$) determination of non-maximal ${\theta }_{23}$ is possible in DUNE in total 7 years if ${\sin }^2{\theta }_{23}\lesssim 0.465(0.450)$ or ${\sin }^2{\theta }_{23}\gtrsim 0.554(0.572)$ for any value of ${\delta }_{CP}$ and NMO. We study the individual contributions from appearance and disappearance channels, impact of systematic uncertainties and marginalization over oscillation parameters, importance of spectral analysis and data from both $\nu$ and $\bar{\nu }$ runs, while analyzing DUNE's sensitivity to establish non-maximal ${\theta }_{23}$. DUNE can resolve the octant of ${\theta }_{23}$ at 4.2$\sigma$ (5$\sigma$) using 7 (10) years of run assuming ${\sin }^2{\theta }_{23}$ = 0.455, ${\delta }_{CP}$ = $223^{\circ }$, and NMO. DUNE can improve the current relative 1$\sigma$ precision on ${\sin }^2{\theta }_{23}$ ($\Delta m_{31}^2$) by a factor of 4.4 (2.8) using 7 years of run.

38 pages, 14 figures, 5 tables. Comments are welcome

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