Search for invisible decays of the Λ baryon

A search for invisible decays of the Λ baryon is carried out in the process J /ψ →Λ Λ ¯ based on (1.0087 ±0.0044 )×10¹⁰ J /ψ events collected with the BESIII detector located at the BEPCII storage ring. No signals are found for the invisible decays of Λ 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.