Author(s): M. Ablikim et al. (BESIII Collaboration) We report an experimental investigation of the reactions $\overline{n}p→2{π}^{+}{π}^{−}$, $\overline{n}p→2{π}^{+}{π}^{−}{π}^{0}$, and $\overline{n}p→2{π}^{+}{π}^{−}2{π}^{0}$ using $(10.087±0.044)×{10}^{9}\text{ }\text{ }J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The a… [Phys. Rev. Lett. 137, 031902] Published Tue Jul 14, 2026