First measurement of muon-neutrino disappearance in NOvA

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