First measurement of muon-neutrino disappearance in NOvA

This paper reports the first measurement using the NOvA detectors of ν_μ disappearance in a ν_μ beam. The analysis uses a 14 kton-equivalent exposure of 2.74×10²⁰ protons-on-target from the Fermilab NuMI beam. Assuming the normal neutrino mass hierarchy, we measure Δm₃₂²=(2.52_-0.18+0.20)×10^-3 eV² and sin²θ₂₃ in the range 0.38--0.65, both at the 68% confidence level, with two statistically degenerate best-fit points at sin²θ₂₃=0.43 and 0.60. Results for the inverted mass hierarchy are also presented.