pp final state interaction in J/ψ →γpp

The phenomenon of the near ppˉ-threshold enhancement observed in the J/ψ→γ pp decay is studied by using the enhancement factor method with a simpler one-pion-exchange potential between p and p. The Jost function caused by the mentioned potential is perturbatively calculated in the zero-th order approximation, and the corresponding enhancement factor is obtained. It is found that such a final state interaction offers an important contribution to the decay width near the ppˉ-threshold, although it is not large enough. To explain the decay data, a phenomenological factor G(p) with the form of 285500/(m 2 π + p 2 ) should be introduced. A further calculation including the p-dependent bare T -matrix, a more realistic N ˉ N potential and the contribution from the higher-order wave functions would provide a better understanding of the decay data and even the existence of the baryonium ppˉ. The near ppˉ-threshold behavior of the decay width in the J/ψ→π 0 pp process is also discussed.