Measurement of the neutrino mixing angle $\hat{I}{¸}_{23}$ in NOvA

Abstract

This Letter reports new results on muon neutrino disappearance from NOvA, using a 14 kton detector equivalent exposure of $6.05\times 10^{20}$ protons-on-target from the NuMI beam at the Fermi National Accelerator Laboratory. The measurement probes the muon-tau symmetry hypothesis that requires maximal mixing ($\hat{I}{¸}_{23}=\ddot{I}€/4$). Assuming the normal mass hierarchy, we find $\hat{I}”m^2=(2.67\pm 0.11)\times 10^{-3}$ eV${}^2$ and ${\sin }^2\hat{I}{¸}_{23}$ at the two statistically degenerate values $0.404_{-0.022}^{+0.030}$ and $0.624_{-0.030}^{+0.022}$, both at the 68% confidence level. Our data disfavor the maximal mixing scenario with 2.6 $\ddot{I}ƒ$ significance.

7 pages, 3 figures