Near Threshold Enhancement of p pbar System and p pbar Elastic Scattering

The observed enhancement of $p\bar{p}$-production near the threshold in radiative decays of $J\mathrm{/}\psi$ and $e^{+}{e}^{-}$-annihilations can be explained with final state interactions among the produced $N\bar{N}$ system, where the enhancement is essentially determined by $N\bar{N}$ elastic scattering amplitudes. We propose to use an effective theory for interactions in a $N\bar N$ system near its threshold. The effective theory is similar to the well-known one for interactions in a $NN$ 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 $J\mathrm{/}\psi$ and $e^{+}{e}^{-}$-annihilations, and the $p\bar{p}$ elastic scattering near the threshold.