Proton-antiproton annihilation in baryonium

A possible interpretation of the near-threshold enhancement in the (pp̄) mass spectrum in J/ψ→γpp̄ is the existence of a narrow baryonium resonance X(1860). Mesonic decays of the (pp̄) bound state $X(1860)$ because of the nucleon-antinucleon annihilation are investigated in this article. Mesonic coherent states with fixed G parity and P parity have been constructed. The Amado-Cannata-Dedoder-Locher-Shao formulation is extended to the decays of the $X(1860)$. By this method, the branch-fraction ratios of Br(X→η4π),Br(X→η2π), and Br(X→3η) are calculated. It is shown that if the $X(1860)$ is a bound state of (pp̄), the decay channel (X→η4π) is favored over (X→η2π). In this way, we develop criteria for distinguishing the baryonium interpretation for the near-threshold enhancement effects in the (pp̄) mass spectrum in J/ψ→γpp̄ from other possibilities. Experimental checks are expected. An intuitive picture for our results is discussed.