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

Using $(1.0087\pm 0.0044)\times {10}^{10}$ $J\mathrm{/}\psi$ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays ${\mathrm{\Xi }}^0\to K^{-}{e}^{+}$ with $\mathrm{\Delta }(B-L)=0$ and ${\mathrm{\Xi }}^0\to K^{+}{e}^{-}$ with $\mathrm{\mid }\mathrm{\Delta }(B-L)\mathrm{\mid }=2$, 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 $\mathcal{B}({\mathrm{\Xi }}^0\to K^{-}{e}^{+})<3.6\times {10}^{-6}$ and $\mathcal{B}({\mathrm{\Xi }}^0\to K^{+}{e}^{-})<1.9\times {10}^{-6}$ at the 90% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.