Exclusive Hadronic D Decays to η ′ and η

Hadronic decay modes D0 → (K,K)(η, η′) and (D+,D+ s ) → (π+, ρ+)(η, η′) are studied in the generalized factorization approach. Form factors for (D,D+ s ) → (η, η′) transitions are carefully evaluated by taking into account the wave function normalization of the η and η′. The predicted branching ratios are generally in agreement with experiment except for D0 → Kη′, D+ → π+η and D+ s → ρ+η′; the calculated decay rates for the first two decay modes are too small by an order of magnitude. We show that the weak decays D0 → K−π+ and D+ → K+K followed by resonance-induced final-state interactions (FSI), which are amenable technically, are able to enhance the branching ratios of D0 → Kη′ and D+ → π+η dramatically without affecting the agreement between theory and experiment for D0 → Kη and D+ → π+η′. We argue that it is difficult to understand the observed large decay rates of D+ s → ρ+η′ and ρ+η simultaneously; FSI, W -annihilation and the production of excess η′ from gluons are not helpful in this regard. The large discrepancy between the factorization hypothesis and experiment for the ratio of D+ s → ρ+η′ and D+ s → η′e+ν remains as an enigma.