Search for active-sterile antineutrino mixing using neutral-current interactions with the NOvA experiment

Abstract

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 km and 810 km from the beam source, is analyzed using an exposure of $12.51\times 10^{20}$ 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 $122\pm 11$(stat.)$\pm 15$(syst.) assuming mixing between three active flavors. No evidence for $\bar{\hat{I}}{½}_{\hat{I}}¼\to \bar{\hat{I}}{½}_s$ oscillation is observed. Interpreting this result within a 3+1 model, constraints are placed on the mixing angles $\hat{I}{¸}_{24}<25^{\circ }$ and $\hat{I}{¸}_{34}<32^{\circ }$ at the 90% C.L. for $0.05$eV${}^2\le \hat{I}”m_{41}^2\le 0.5$eV${}^2$, 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.

8 pages, 4 figures