An Explanation for the rho-pi Puzzle of J/psi and psi' Decays

Abstract

We propose a new explanation for the longstanding puzzle of the tiny branching fraction of psi' -> rho pi relative to that for J/psi -> rho pi. In the case of J/psi, we argue that this decay is dominated by a higher Fock state in which the ccbar pair is in a color-octet ^3S_1 state and via annihilate process ccbar -> qqbar. In the case of the psi', we argue that the probability for the ccbar pair in this higher Fock state to be close enough to annihilate is suppressed by a dynamical effect related to the small energy gap between the mass of the psi' and the DDbar threshold.