Search for baryon and lepton number violating decays of ${\Xi }^{0}$ hyperons

Using $\left(1.0087±0.0044\right)×{10}^{10}\text{}\text{}J/\psi $ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays ${\Xi }^{0}\to {K}^{-}{e}^{+}$ with $\Delta \left(B-L\right)=0$ and ${\Xi }^{0}\to {K}^{+}{e}^{-}$ with $|\Delta \left(B-L\right)|=2$, where $B$ ($L$) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to $B\left({\Xi }^{0}\to {K}^{-}{e}^{+}\right)<3.6×{10}^{-6}$ and $B\left({\Xi }^{0}\to {K}^{+}{e}^{-}\right)<1.9×{10}^{-6}$ at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.