Near threshold enhancement of pp¯ system and pp¯ elastic scattering

The observed enhancement of pp¯-production near the threshold in radiative decays of J/ψ and e+e−-annihilations can be explained with final state interactions among the produced NN¯ system, where the enhancement is essentially determined by NN¯ elastic scattering amplitudes. We propose to use an effective theory for interactions in an NN¯ system near its threshold. The effective theory is similar to the well-known one for interactions in an NN system but with distinctions. It is interesting to note that in the effective theory some corrections to scattering amplitudes at tree-level can systematically be summed into a simple form. These corrections are from rescattering processes. With these corrected amplitudes we are able to describe the enhancement near the threshold in radiative decays of J/ψ and e+e−-annihilations, and the pp¯ elastic scattering near the threshold.