We report results from the first search for sterile neutrinos mixing with active neutrinos through a reduction in the rate of neutral-current interactions over a baseline of 810 km between the NOvA detectors. Analyzing a 14-kton detector equivalent exposure of $6.05\times {10}^{20}$ protons-on-target in the NuMI beam at Fermilab, we observe 95 neutral-current candidates at the Far Detector compared with $83.5\pm 9.7(\mathrm{stat})\pm 9.4(\mathrm{syst})$ events predicted assuming mixing only occurs between active neutrino species. No evidence for ${\nu }_{\mu }\to {\nu }_s$ transitions is found. Interpreting these results within a $3+1$ model, we place constraints on the mixing angles ${\theta }_{24}<20.8°$ and ${\theta }_{34}<31.2°$ at the 90% C.L. for $0.05{\mathrm{eV}}^2\le \mathrm{\Delta }{m}_{41}^2\le 0.5{\mathrm{eV}}^2$, the range of mass splittings that produce no significant oscillations over the Near Detector baseline.

• Received 16 June 2017

DOI:https://doi.org/10.1103/PhysRevD.96.072006