Search for active-sterile neutrino mixing using neutral-current interactions in NOvA

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 $6.05\ifmmode\times\else\texttimes\fi{}{10}^{20}$ protons-on-target in the NuMI beam at Fermilab, we observe 95 neutral-current candidates at the Far Detector compared with $83.5\ifmmode\pm\else\textpm\fi{}9.7(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}9.4(\mathrm{syst})$ events predicted assuming mixing only occurs between active neutrino species. No evidence for ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s}$ transitions is found. Interpreting these results within a $3+1$ model, we place constraints on the mixing angles ${\ensuremath{\theta}}_{24}<20.8\ifmmode^\circ\else\textdegree\fi{}$ and ${\ensuremath{\theta}}_{34}<31.2\ifmmode^\circ\else\textdegree\fi{}$ at the 90% C.L. for $0.05\text{ }\text{ }{\mathrm{eV}}^{2}\ensuremath{\le}\mathrm{\ensuremath{\Delta}}{m}_{41}^{2}\ensuremath{\le}0.5\text{ }\text{ }{\mathrm{eV}}^{2}$, the range of mass splittings that produce no significant oscillations over the Near Detector baseline.