Study of the reactions $\bar{n}p\to 2{\pi }^{+}{\pi }^{-}$, $2{\pi }^{+}{\pi }^{-}{\pi }^0$, and $2{\pi }^{+}{\pi }^{-}2{\pi }^0$ using $J\mathrm{/}\psi \to p{\pi }^{-}\bar{n}$

We report an experimental investigation of the reactions $\bar{n}p\to 2{\pi }^{+}{\pi }^{-}$, $\bar{n}p\to 2{\pi }^{+}{\pi }^{-}{\pi }^0$, and $\bar{n}p\to 2{\pi }^{+}{\pi }^{-}2{\pi }^0$ using $(10.087\pm 0.044)\times {10}^9$ $J\mathrm{/}\psi$ events collected with the BESIII detector at the BEPCII storage ring. The antineutron ($\bar{n}$) is produced in the decay $J\mathrm{/}\psi \to p{\pi }^{-}\bar{n}$ with studied momentum from 200~MeV/$c$ to 1174~MeV/$c$, while the target proton originates from the hydrogen nuclei in the cooling oil of the beam pipe. This novel method pioneers the study of $\bar{n}$-nucleon interactions at an $e^{+}{e}^{-}$ collider, providing the first experimental data for $\bar{n}$ momenta exceeding 800~MeV/$c$.