This paper reports the first measurement using the NOvA detectors of $\nu_\mu$ disappearance in a $\nu_\mu$ beam. The analysis uses a 14 kton-equivalent exposure of $2.74 \times 10^{ 20}$ protons-on-target from the Fermilab NuMI beam. Assuming the normal neutrino mass hierarchy, we measure $\Delta m^{ 2}_{ 32}=(2.52^{ +0.20}_{ -0.18})\times 10^{ -3}$ eV$^{ 2}$ and $\sin^2\theta_{ 23}$ in the range 0.38-0.65, both at the 68% confidence level, with two statistically-degenerate best fit points at $\sin^2\theta_{ 23} = $ 0.43 and 0.60. Results for the inverted mass hierarchy are also presented.
Categories: hep-ex physics.ins-det