Photon or meson formation in $J/\ddot{I}ˆ$ decays into $p\overline{p}$

Abstract

The measurements of the $J/\ddot{I}ˆ\to {\hat{I}}^{3}p\overline{p}$ decays by the BES Collaboration indicate an enhancement at the $p\overline{p}$ threshold which, however, is not present in the J/$\ddot{I}ˆ$ decays into $\ddot{I}‰p\overline{p}$ and into $\ddot{I}€p\overline{p}$. Here, two processes for describing the decays $J/\ddot{I}ˆ\to \mathcal{B}p\overline{p}$ where $\mathcal{B}={\hat{I}}^3,\ddot{I}‰$ are presented in some detail and the cases $\mathcal{B}=\ddot{I}•,\ddot{I}€$ are briefly touched on. The first one, applied not only to the radiative decay to reproduce the threshold peak but also to the $\ddot{I}‰p\overline{p}$ decay channel to improve the description of the spectrum, postulates a direct emission of the boson before the baryon pair is formed. The second process assumes that the boson $\mathcal{B}$ is emitted from the baryon pair following the $J/\ddot{I}ˆ$ decay and includes for the decays into ${\hat{I}}^{3}p\overline{p}$ a final state nucleon-antinucleon interaction based on the Paris $N\overline{N}$ potential. The reproduction of the $p\overline{p}$ distribution in the $J/\ddot{I}ˆ\to \ddot{I}‰p\overline{p}$ decays needs a final state interaction involving a $N(2050)3/2^{-}$ resonance. The photon- and meson-emission rates are reproduced in a semi-quantitative way.

37 pages, 5 tables and 10 figures. Extended discussions, one more figure and several references added