Improved Limits on Light Sterile Neutrino Mixing from Disappearance Searches at Daya Bay, MINOS/MINOS+, and Bugey-3

Reactor neutrino experiments are well-suited for probing the existence of a light sterile neutrino in the region of a sub-eV$^2$ mass splitting. Using eight functionally identical antineutrino detectors, the Daya Bay experiment measures the electron antineutrinos produced by six nuclear reactors located near Shenzhen, China. A 1230-day sample of antineutrinos was used to set the most stringent limits to date on the mixing of sterile neutrinos for $2\times 10^{-4}\, < \Delta m^2_{41} < 0.3$ eV$^2$, based on two independent statistical methods, Feldman-Cousins and CL$_{\mathrm{s}}$, which gave consistent results. Going further, sensitivity was extended to larger $\Delta m^2_{41}$ using data from the Bugey-3 short-baseline reactor experiment and MINOS/MINOS+ accelerator experiments. The joint analysis excludes the LSND and MiniBooNE allowed regions for $\Delta m^2_{41} < 5$ $(1.2)$ eV$^2$ at $90\%$ $(99\%)$ C.L., strongly increasing the tension between a four-flavor interpretation of their observations and the null results of other experiments.