Search for a sub-eV sterile neutrino using Daya Bay's full dataset

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This Letter presents results of a search for the mixing of a sub-eV sterile neutrino based on the full data sample of the Daya Bay Reactor Neutrino Experiment, collected during 3158 days of detector operation, which contains 5.55 × 10⁶ reactor candidates identified as inverse beta-decay interactions followed by neutron-capture on gadolinium. The result was obtained in the minimally extended 3+1 neutrino mixing model. The analysis benefits from a doubling of the statistics of our previous result and from improvements of several important systematic uncertainties. The results are consistent with the standard three-neutrino mixing model and no significant signal of a sub-eV sterile neutrino was found. Exclusion limits are set by both Feldman-Cousins and CLs methods. Light sterile neutrino mixing with sin² 2θ₁₄ 0.01 can be excluded at 95% confidence level in the region of $0.01$ eV² |Δ m²₄₁| 0.1 eV². This result represents the world-leading constraints in the region of 2 × 10⁻⁴ eV² |Δ m²₄₁| 0.2 eV².