Exclusive decays of heavy mesons

Abstract

In order to describe quantitatively the strong or weak decays of heavy particles into two π(K)-mesons one needs to know the behaviour of the π-meson wave function ϕ π ( x) which determines the quark longitudinal momentum distribution inside the π-meson, p 1 = xp π , p 2 = (1 − x) p π , p π → ∞). We calculate the few first moments 〈 ξ 2 n 〉 ≡ ∫ −1 1 d ξξ 2 n ϕ π ( ξ), ξ = 2 x − 1 of the π-meson wave function using the QCD sum rules, and show that sum rules give strong restrictions on the values of the moments 〈 ξ 2 n 〉. Based on these results we discuss the qualitative behaviour of ϕ π ( x) and propose the model wave function. It is shown that this model wave function which fulfills the QCD sum rules gives a good description of the π-meson strong decay modes of the S and P charmonium levels. The two-particle weak decays of the D(F) mesons into π (and/or K) mesons are considered as well. It is shown that the annihilation contributions play an essential role in these decays (because of the earlier found properties of the π(K)-meson wave functions). Estimates of the Cabibbo-allowed and the Cabibbo-suppressed decat widths are presented (D → K π, KK, ππ,…). All the predictions for the strong, electromagnetic and weak two-particle decay widths are consistent with the available experimental data.