Parity, Charge Conjugation and SU(3) Constraints on Threshold Enhancement in $J/ψ$ decays into $γp\bar p$ and $K p \barΛ$

Abstract

We study the threshold enhancement effects of baryon-anti-baryon systems in $J/ψ$ 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 $J/ψ\to γp\bar p$ to be in a state with $C=+1$, while the $p\bar p$ in $J/ψ\to π^0 p\bar p$ 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 $Λ\bar p$ system cannot be in $0^+$ and $0^-$ states in $J/ψ\to K^+ Λ\bar p$. We provide a consistent explanation of observation and non-observation of near threshold enhancements in $J/ψ\to K^+ Λ\bar p$ and $J/ψ\to π^0 p \bar p$, respectively. We also find that near baryon pair threshold enhancement can happen in several channels for $J/ψ$ decays and can be several times larger than that observed in $J/ψ\to K^+ Λ\bar p$ in some channels.