Long distance contributions in

Cabibbo allowedD→Kπγdecays

“…When one compares the results obtained here for the radiative decays to nonresonant Kπ, with those previously obtained for the D → K * γ [4,6,7,16], it emerges that the nonresonant channel is the more frequent one. Thus, while one expects for D + → K * + γ a branching ratio (BR) of about 10 −6 (this decay being doubly Cabibbo suppressed), the direct decay D + →K 0 π + γ is expected to have a BR of ≃ 3 × 10 −5 in our model.…”

“…In the charm radiative decays, the theoretical studies show that likewise, the long -distance is the dominant feature of the decays [2,4,6,7,9]. The short -distance contribution realized by the penguin diagram c → uγ [14,15,16] might play a role in certain Cabibbo suppressed decays, which are not discussed in the present paper.…”

“…The radiative decays D 0 → ρ 0 , ω 0 , φ,K * 0 +γ were recently bounded [5] to branching ratios in the 10 −4 range, which is approaching the standard model expectations (see, e.g. [6,7] where additional previous works are mentioned). The dilepton decays D → P l + l − , D → V l + l − are the subject of intensive searches at CLEO and Fermilab [8].…”

“…We are interested in the role played by the vector mesons in these decays; obviously not in the direct Kπ channel, which belongs to D 0 →K * 0 γ and was treated separately [6,7,16] , and others). This is the main reason for our using an effective Lagrangian which contains the light vector mesons [23].…”

Radiative decay modes of theD0meson

“…If the coupling of the photon to the transverse component of a ρ 0 results in a vector conversion with about 1% probability, we can use the Particle Data Group [3] value for the D 0 → φρ branching ratio, (2.6 ± 0.8) × 10 −3 , and expect that BR(D 0 → φγ) is about 2.6 × 10 −5 · f T , where f T is the fraction of ρ's produced in the decay of the D 0 which are transversely polarized. Detailed calculations of the long-range, W -exchange and other contributing processes have been published by several groups [4][5][6][7][8]. The predictions range from 10 −4 to 10 −6 and are listed in Table I. In the b sector, observation of the decay B → K * γ at the measured rate provided compelling evidence for the existence of a "penguin" contribution to the B mesons decay amplitude into this channel.…”