Parity, Charge Conjugation and SU(3) Constraints on Threshold Enhancement in $J/\psi$ decays into $\gamma p\bar{p}$ and $Kp\bar{\Lambda }$

Abstract

We study the threshold enhancement effects of baryon-anti-baryon systems in $J/\psi$ decays at BES using parity $P$, charge conjugation $C$, and flavor SU(3) symmetries. The $P$ and $C$ symmetries restrict the $p\bar{p}$ in $J/\psi \to \gamma p\bar{p}$ to be in a state with $C=+1$, while the $p\bar{p}$ in $J/\psi \to {\pi }^{0}p\bar{p}$ to be with $C=-1$. Combining the $C$ and $P$ symmetries with flavor SU(3) symmetry, i.e. the CPS symmetry, we find that the $\Lambda \bar{p}$ system cannot be in $0^{+}$ and $0^{-}$ states in $J/\psi \to K^{+}\Lambda \bar{p}$. We provide a consistent explanation of observation and non-observation of near threshold enhancements in $J/\psi \to K^{+}\Lambda \bar{p}$ and $J/\psi \to {\pi }^{0}p\bar{p}$, respectively. We also find that near baryon pair threshold enhancement can happen in several channels for $J/\psi$ decays and can be several times larger than that observed in $J/\psi \to K^{+}\Lambda \bar{p}$ in some channels.

Latex 10 pages, no figures, typos corrected