There is an accumulation of proof for anomalous habits in the proton-antiproton system near the ppbar mass threshold, e.g., J/ ψ → γppabr, J/ ψ → γπ+ π– η and the protons effective form factor figured out from e+ e– → ppbar, showing a narrow peak or an extremely high falloff around the ppbar mass limit, which influenced numerous speculations and restored the interests on the nucleon-antinucleon bound state.Fig. 2: The anomalous line shape of the resonant structure around ppbar mass limit in 3( π+ π-) mass spectrum. The distance of its mass to the ppbar mass threshold supports the existence of a ppbar bound state.
There is an accumulation of evidence for anomalous habits in the proton-antiproton system near the ppbar mass limit, e.g., J/ ψ → γppabr, J/ ψ → γπ+ π– η and the protons reliable type factor determined from e+ e– → ppbar, displaying a narrow peak or an extremely steep falloff around the ppbar mass threshold, which motivated numerous speculations and renewed the interests on the nucleon-antinucleon bound state.Fig. 2: The anomalous line shape of the resonant structure around ppbar mass threshold in 3( π+ π-) mass spectrum. The distance of its mass to the ppbar mass limit supports the existence of a ppbar bound state.