Parity, charge conjugation, and SU(3) constraints on threshold enhancement in J/psi decays into gamma p(p)over-bar and Kp(Lambda)over-bar

We study the threshold enhancement effects of baryon-antibaryon 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 (p) over bar in J/psi-->gammap (p) over bar to be in a state with C=+1, while the p (p) over bar in J/psi-->pi(0)p (p) over bar 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(p) over bar system cannot be in 0(+) and 0(-) states in J/psi-->K(+)Lambda(p) over bar. We provide a consistent explanation of observation and nonobservation of near threshold enhancements in J/psi-->K(+)Lambda(p) over bar and J/psi-->pi(0)p (p) over bar, 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-->K(+)Lambda(p) over bar in some channels.