An Explanation for theρ−πPuzzle ofJ/ψandψ′Decays

Abstract

We propose a new explanation for the long-standing puzzle of the tiny branching fraction of ${\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\pi}$ relative to that for $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\pi}$. In the case of $J/\ensuremath{\psi}$, we argue that this decay is dominated by a higher Fock state in which the $c\overline{c}$ pair is in a color-octet $^{3}S_{1}$ state and decays via the annihilation process $c\overline{c}\ensuremath{\rightarrow}q\overline{q}$. In the case of the ${\ensuremath{\psi}}^{\ensuremath{'}}$, we argue that the probability for the $c\overline{c}$ 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 ${\ensuremath{\psi}}^{\ensuremath{'}}$ and the $D\overline{D}$ threshold.