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 6.05×10²⁰ protons-on-target in the NuMI beam at Fermilab, we observe 95 neutral-current candidates at the Far Detector compared with 83.5±9.7(stat)±9.4(syst) events predicted assuming mixing only occurs between active neutrino species. No evidence for ν_μ→νₛ transitions is found. Interpreting these results within a $3+1$ model, we place constraints on the mixing angles θ₂₄<20.8^∘ and θ₃₄<31.2^∘ at the 90% C.L. for 0.05 eV²≤Δm₄₁²≤0.5 eV², the range of mass splittings that produce no significant oscillations over the Near Detector baseline.