This Letter reports results from the first long-baseline search for sterile antineutrinos mixing in an accelerator-based antineutrino-dominated beam. The rate of neutral-current interactions in the two NOvA detectors, at distances of 1 and 810 km from the beam source, is analyzed using an exposure of 12.51×1020 protons-on-target from the NuMI beam at Fermilab running in antineutrino mode. A total of 121 of neutral-current candidates are observed at the far detector, compared to a prediction of 122±11(stat.)±15(syst.) assuming mixing only between three active flavors. No evidence for ⊽ μ → ⊽ s oscillation is observed. Interpreting this result within a 3+1 model, constraints are placed on the mixing angles θ24 < 25° and θ34<32° at the 90% C.L. for 0.05 eV2 ≤ Δm2 41 ≤0.5 eV2, the range of mass splittings that produces no significant oscillations at the near detector. These are the first 3+1 confidence limits set using long-baseline accelerator antineutrinos.
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Preprint version Physical Review Letters, Volume 127, Issue 20, 2021, pages 201801-.
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Acero, M. A., Adamson, P., Aliaga, L., Anfimov, N., Antoshkin, A., Arrieta-Diaz, E., Asquith, L., Aurisano, A., Back, A., Backhouse, C., Baird, M., Balashov, N., Baldi, P., Bambah, B. A., Bashar, S., Bays, K., Bernstein, R., Bhatnagar, V., Bhuyan, B., & Bian, J. (2021b). Search for Active-Sterile Antineutrino Mixing Using Neutral-Current Interactions with the NOvA Experiment. Physical Review Letters, 127(20). https://doi.org/10.1103/physrevlett.127.201801