Search for new physics with baryons at BESIII

The BESIII experiment at BEPCII provides a clean environment to test baryon-dark sector connections and baryon-number violation. Using $10^{10}$ $J/ψ$ events, searches were performed for $Σ^{+}\to p+\text{inv}$, $Ξ^{-}\toπ^{-}+\text{inv}$, and $\barΛ-Λ$ oscillations. No excess was observed, yielding $\mathcal{B}(Σ^{+}\to p+\text{inv})<3.2\times10^{-5}$, $\mathcal{B}(Ξ^{-}\toπ^{-}+\text{inv})<(4-7)\times10^{-5}$, and $P(Λ)<4.4\times10^{-6}$ (90\% C.L.). These are the most stringent limits on invisible baryon decays and $ΔB=2$ transitions in strange baryons, probing new physics beyond the Standard Model.