# Measurement of the neutrino mixing angle $\theta_{23}$ in NOvA

## TL;DR

This paper reports new measurements of the neutrino mixing angle θ23 using NOvA data, providing evidence against maximal mixing and refining the parameters of neutrino oscillations.

## Contribution

First measurement of θ23 and Δm² using NOvA muon neutrino disappearance data with high statistical significance.

## Key findings

- Disfavors maximal mixing with 2.6 σ significance
- Measures Δm² = (2.67 ± 0.11)×10⁻³ eV²
- Finds two degenerate values of sin²θ23 at 68% CL

## Abstract

This Letter reports new results on muon neutrino disappearance from NOvA, using a 14 kton detector equivalent exposure of $6.05\times10^{20}$ 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 ($\theta_{23} = \pi/4$). Assuming the normal mass hierarchy, we find $\Delta m^2 = (2.67 \pm 0.11)\times 10^{-3}$ eV$^2$ and $\sin^2 \theta_{23}$ at the two statistically degenerate values $0.404^{+0.030}_{-0.022}$ and $0.624^{+0.022}_{-0.030}$, both at the 68% confidence level. Our data disfavor the maximal mixing scenario with 2.6 $\sigma$ significance.