Fen Zuo

Semileptonic Bc decays and charmonium distribution amplitude

In this paper we study the semileptonic decays of the Bc meson in the light-cone sum rule (LCSR) approach. The result for each channel depends on the corresponding distribution amplitude (DA) of the final meson. For the case of Bc decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist distribution amplitude is involved if we start from a chiral current. If we choose a suitable chiral current in the vector meson case, the main twist-3 contributions are also eliminated and we can consider the leading twist contribution only. The leading twist distribution amplitudes of the charmonium and other heavy mesons are given by a model approach in a reasonable way. Employing this charmonium distribution amplitude we find a cross section

The cross section of the process e ++e −→J/ψ+η c within the QCD light-cone sum rules

\sigma(e^+e^-\to{}J/\psi+\eta_c)\simeq{22.8}\text{fb}

Couplings of the rho meson in a holographic dual of QCD with Regge trajectories

that is consistent with Belle and BaBar data. Based on this model, we calculate the form factors for various Bc decay modes in the corresponding regions. Extrapolating the form factors to the whole kinetic regions, we get the decay widths and branching ratios for various Bc decay modes including their τ modes when they are kinematically accessible.

Form factor for B→Dlν˜ in the light-cone sum rules with chiral current correlator

We calculate the cross section of the exclusive process e++e−→J/ψ+ηc at the leading order approximation within the QCD light-cone sum rules approach. It is found that the form factor FVP(V=J/ψ,P=ηc) depends mainly on the behavior of the twist-2 distribution amplitude of the ηc meson at the scale of this process. Thus in order to obtain a reliable estimation of the cross section, it is important to have a realistic distribution amplitude of the ηc meson and to deal with the evolution of the distribution amplitude to the effective energy scale of the process. Our results show that one can obtain a compatible prediction with the Belle and BaBar experimental data.

Heavy-to-light transition form factors and their relations in light-cone QCD sum rules

The couplings gρHH of the ρ meson with a scalar meson H are calculated in a holographic dual of QCD in which the Regge trajectories for the mesons are manifest. In contrast to the conclusion in general AdS/QCD models, the resulting couplings grow linearly with the quantum number of excited H; thus they are far from universal. This non-universality seems to result from the disappearance of an explicit cutoff in the holographic dimension in this model. Correspondingly, the ρ-dominance for the electromagnetic form factors of H does not hold any more, even in an apparent sign-alternating manner. With these couplings at hand, the asymptotic behavior of the form factors can easily be calculated. The form factor exhibits the 1/Q(2Δ-2) behavior, which is in accordance with the scaling behavior of the fixed-angle scattering amplitude based on the AdS/CFT correspondence. It is also pointed out that the asymptotic behavior can be matched to the results of perturbative QCD, if the conformal dimension Δ of the operator is replaced by the combination τ+L of the meson.

Semileptonic

Abstract Within the framework of QCD light-cone sum rules (LCSR), we calculate the form factor for B → D l ν ˜ transitions with chiral current correlator. The resulting form factor depends on the distribution amplitude (DA) of the D-meson. We try to use three kinds of DA models of the D-meson. In the velocity transfer region 1.14 y 1.59 , which renders the operator product expansion (OPE) near light-cone x 2 = 0 go effectively, the yielding behavior of form factor is in agreement with that extracted from the data on B → D l ν ˜ , within the error. In the large recoil region 1.35 y 1.59 , the results are observed consistent with those of perturbative QCD (pQCD). The presented calculation can play a bridge role connecting those from the lattice QCD, heavy quark symmetry and pQCD to have an all-around understanding of B → D l ν ˜ transitions.

B(B_s, B_c)

The light-cone QCD sum rules approach improved by using the chiral current correlator is systematically reviewed and applied to the calculation of all the heavy-to-light form factors, including all the semileptonic and penguin ones. By choosing suitable chiral currents, the light-cone sum rules for all the form factors are greatly simplified and depend mainly on one leading-twist distribution amplitude of the light meson. As a result, relations between these form factors arise naturally. At the considered accuracy, these relations reproduce the results obtained in the literature. Moreover, since the explicit dependence on the leading-twist distribution amplitudes is preserved, these relations may be more useful to simulate the experimental data and extract information on the distribution amplitude.

decays in the light-cone QCD sum rules

Semileptonic B(Bs, Bc) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several B(Bc) decay modes of current interest.

Semileptonic B(B(s), B(c)) decays in the light-cone QCD sum rules

Semileptonic B(Bs, Bc) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several B(Bc) decay modes of current interest.

Form Factor for

Abstract Within the framework of QCD light-cone sum rules (LCSR), we calculate the form factor for B → D l ν ˜ transitions with chiral current correlator. The resulting form factor depends on the distribution amplitude (DA) of the D-meson. We try to use three kinds of DA models of the D-meson. In the velocity transfer region 1.14 y 1.59 , which renders the operator product expansion (OPE) near light-cone x 2 = 0 go effectively, the yielding behavior of form factor is in agreement with that extracted from the data on B → D l ν ˜ , within the error. In the large recoil region 1.35 y 1.59 , the results are observed consistent with those of perturbative QCD (pQCD). The presented calculation can play a bridge role connecting those from the lattice QCD, heavy quark symmetry and pQCD to have an all-around understanding of B → D l ν ˜ transitions.