Addendum on Resonant Final-State Interactions

For hadronic two-body decays of charmed mesons involving η or η′, resonance-induced finalstate interactions (FSI) that mimic the W -exchange or the W -annihilation topology can play an essential role. In particular, the decays D0 → Kη′ and D+ → π+η, which are largely suppressed in the absence of FSI, are enhanced dramatically by resonant FSI. It is stressed that the effect of resonant FSI is negligible for ρ+(η, η′) final states because of the mismatch of the G parity of ρ+(η, η′) and the J = 0, I = 1 meson resonance. We argue that a possible gluon-mediated process in which two gluons couple directly to the gluonic component of the η′, e.g. the gluonium, rather than to the flavor-singlet η0, can enhance both modes D + s → ρ+η′ and D+ s → ρ+η, especially the former; that is, this new mechanism can account for the unexpectedly large branching ratio of ρ+η′ without suppressing ρ+η.