Nucleon pole contributions in $J/\psi \to N \bar N \pi$, $p \bar p \eta$, $p \bar p \eta^{ \prime}$ and $p \bar{ p} \omega$ decays are re-studied. Different contributions due to PS-PS and PS-PV couplings in the $\pi$-N interaction and the effects of $NN\pi$ form factors are investigated in the $J/\psi \to N \bar N \pi$ decay channel. It is found that when the ratio of $|F_0| /|F_M|$ takes small value, without considering the $NN\pi$ form factor, the difference between PS-PS and PS-PV couplings are negligible. However, when the $NN\pi$ form factor is included, this difference is greatly enlarged. The resultant decay widths are sensitive to the form factors. As a conclusion, the nucleon-pole contribution as a background is important in the $J/\psi\to N\bar{ N}\pi$ decay and must be accounted. In the $J/\psi\to N\bar{ N}\eta$ and $N\bar{ N}\eta'$ decays, its contribution is less than 0.1% of the data. In the $J/\psi\to N\bar{ N}\omega$ decay, it provides rather important contribution without considering form factors. But the contribution is suppressed greatly when adding the off-shell form factors. Comparing these results with data would help us to select a proper form factor for such kind of decay.
Categories: nucl-th