First Study of Reaction ${\Xi }^{0}n\to {\Xi }^{-}p$ Using ${\Xi }^{0}$-Nucleus Scattering at an Electron-Positron Collider

Using $\left(1.0087±0.0044\right)×{10}^{10}\text{}\text{}J/\psi $ events collected with the BESIII detector at the BEPCII storage ring, the process ${\Xi }^{0}n\to {\Xi }^{-}p$ is studied, where the ${\Xi }^{0}$ baryon is produced in the process $J/\psi \to {\Xi }^{0}{\overline{\Xi }}^{0}$ and the neutron is a component of the ${}^{9}\mathrm{Be}$, ${}^{12}C$, and ${}^{197}\mathrm{Au}$ nuclei in the beam pipe. A clear signal is observed with a statistical significance of $7.1\sigma $. The cross section of the reaction ${\Xi }^{0}+{}^{9}\mathrm{Be}\to {\Xi }^{-}+p+{}^{8}\mathrm{Be}$ is determined to be $\sigma \left({\Xi }^{0}+{}^{9}\mathrm{Be}\to {\Xi }^{-}+p+{}^{8}\mathrm{Be}\right)=\left(22.1±{5.3}_{\mathrm{stat}}±{4.5}_{\mathrm{sys}}\right)\text{}\text{}\mathrm{mb}$ at the ${\Xi }^{0}$ momentum of $0.818\text{}\text{}\mathrm{GeV}/c$, where the first uncertainty is statistical and the second is systematic. No significant $H$-dibaryon signal is observed in the ${\Xi }^{-}p$ final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.