Search for invisible decays of the $\Lambda $ baryon

A search for invisible decays of the $\Lambda $ baryon is carried out in the process $J/\psi \to \Lambda \overline{\Lambda }$ based on $\left(1.0087±0.0044\right)×{10}^{10}\text{}\text{}J/\psi $ events collected with the BESIII detector located at the BEPCII storage ring. No signals are found for the invisible decays of $\Lambda $ baryon, and the upper limit of the branching fraction is determined to be $7.4×{10}^{-5}$ at the 90% confidence level. This is the first search for invisible decays of baryons; such searches will play an important role in constraining dark sector models related to the baryon asymmetry.