pp-bar final state interaction in J/ψ → γpp-bar

The phenomenon of the near pp-bar-threshold enhancement observed in the J/ψ → γpp-bar decay is studied by using the enhancement factor method with a simpler one-pion-exchange potential between p and p-bar. 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 pp-threshold, although it is not large enough. To explain the decay data, a phenomenological factor G(p) with the form of 285500/(mπ2 + p2) should be introduced. A further calculation including the p-dependent bare T-matrix, a more realistic NN 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 pp-bar. The near pp-bar-threshold behavior of the decay width in the J/ψ → π0 pp-bar process is also discussed. (authors)