Search for invisible decays of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math> baryon

A search for invisible decays of the $\mathrm{\ensuremath{\Lambda}}$ baryon is carried out in the process $J/\ensuremath{\psi}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}$ based on $(1.0087\ifmmode\pm\else\textpm\fi{}0.0044)\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }J/\ensuremath{\psi}$ events collected with the BESIII detector located at the BEPCII storage ring. No signals are found for the invisible decays of $\mathrm{\ensuremath{\Lambda}}$ baryon, and the upper limit of the branching fraction is determined to be $7.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ 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.