The recent measurements by the BES Collaboration of $J/\psi$ decays into $\gamma p\overline{p}$ indicate a strong enhancement at $p\overline{p}$ threshold not observed in the decays into ${\pi }^{0}p\overline{p}$. Is this enhancement due to a $p\overline{p}$ quasibound state or a baryonium? A natural explanation follows from a traditional model of $p\overline{p}$ interactions based on the G-parity transformation. The observed $p\overline{p}$ structure is due to a strong attraction in the ${}^1{S}_0$ state and possibly to a near-threshold quasibound state in the ${}^{11}{S}_0$ wave.

• Received 13 January 2005

DOI:https://doi.org/10.1103/PhysRevC.72.011001