On the near-threshold $\bar{p}p$ invariant mass spectrum measured in $J/\psi$ and ${\psi }^{\prime }$ decays

Abstract

A systematic analysis of the near-threshold enhancement in the $\bar{p}p$ invariant mass spectrum seen in the decay reactions $J/\psi \to x\bar{p}p$ and $\psi (3686)\to x\bar{p}p$ $(x=\gamma ,\omega ,\rho ,\pi ,\eta )$ is presented. The enhancement is assumed to be due to the $\bar{N}N$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar{N}N$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar{p}p$ scattering data is considered and, in addition, an older phenomenological model constructed by the Jülich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar{p}p$ FSI. It turns out that the interaction in the isospin-1 ${}^1{S}_0$ channel required for the description of the $J/\psi \to \gamma \bar{p}p$ decay predicts a $\bar{N}N$ bound state.

Comments: 13 pages, 12 figures