First observation of the decay $\hat{I}{›}_c^{+}\to n{K}_S^0\ddot{I}{€}^{+}\ddot{I}{€}^0$

Abstract

Based on 4.5 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data accumulated at center-of-mass energies between $4599.53$ MeV and $4698.82$ MeV with the BESIII detector, the decay $\hat{I}{›}_c^{+}\to n{K}_S^0\ddot{I}{€}^{+}\ddot{I}{€}^0$ is observed for the first time with a significance of $9.2\ddot{I}ƒ$. The branching fraction is measured to be $(0.85\pm 0.13\pm 0.03)\%$, where the first uncertainty is statistical and the second systematic, which differs from the theoretical prediction based on isospin by 4.4$\ddot{I}ƒ$. This indicates that there may be resonant contributions or some unknown dynamics in this decay.