This paper reports the first measurement using the NOvA detectors of νμ disappearance in a νμ beam. The analysis uses a 14 kton-equivalent exposure of 2.74 x 1020 protons-on-target from the Fermilab NuMI beam.
Assuming the normal neutrino mass hierarchy, we measure Δm and sin2 θ23 in the range 0.38-0.65, both at the 68% confidence level, with two statistically degenerate best-fit points at sin2θ. Results for the inverted mass hierarchy are also presented.