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 2.74×10^(20) protons-on-target from the Fermilab NuMI beam. Assuming the normal neutrino mass hierarchy, we measure Δm^2_(32) =(2.52^(+0.20)_(−0.18))×10^(−3) eV^2 and sin^2 θ_(23) in the range 0.38–0.65, both at the 68% confidence level, with two statistically degenerate best-fit points at sin^2 θ_(23) =0.43 and 0.60. Results for the inverted mass hierarchy are also presented.