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 ${10}^{10}$ $J\mathrm{/}\psi$ events, searches were performed for ${\mathrm{\Sigma }}^{+}\to p+\text{inv}$, ${\mathrm{\Xi }}^{-}\to {\pi }^{-}+\text{inv}$, and $\bar{\mathrm{\Lambda }}-\mathrm{\Lambda }$ oscillations. No excess was observed, yielding $\mathcal{B}({\mathrm{\Sigma }}^{+}\to p+\text{inv})<3.2\times {10}^{-5}$, $\mathcal{B}({\mathrm{\Xi }}^{-}\to {\pi }^{-}+\text{inv})<(4-7)\times {10}^{-5}$, and $P(\mathrm{\Lambda })<4.4\times {10}^{-6}$ (90% C.L.). These are the most stringent limits on invisible baryon decays and $\mathrm{\Delta }B=2$ transitions in strange baryons, probing new physics beyond the Standard Model.