arXiv subjects
Publications and source records attributed to Mao-Zhi Yang.
We calculate $B_{(s)}$, and $D_{(s)}$ to $K^*_0(1430)$ transition form factors, and study semileptonic decays of $B_{(s)}$ and $D_{(s)}\to K_0^*(1430) \bar{\ell}ν$ based on QCD sum rule. Measuring these semileptonic decays with high statistics will give valuable information on the nature of light scalar mesons.
The radiative B-> rho gamma, B-> omega gamma decay modes are caused by the FCNC process, so they give us good insight towards probing the standard model in order to search for new physics. In this paper, we compute the branching ratio, direct CP asymmetry, and isospin breaking effects using the perturbative QCD approach within the standard model.
The decay constant of $K_0^*(1430)$ is the key quantity to determine the production rate of $K_0^*(1430)$ in $τ$ decays. By assuming $K_0^*(1430)$ is the lowest scalar bound state of $s\bar{q}$, the decay constant can be calculated reliably in QCD sum rule. Then the decay branching ratio of $τ\to K_0^*(1430)ν$ is predicted to be about $(7.9\pm 3.1)\times 10^{-5}$. If this branching ratio can be measured by experiment, it should be helpful to make clear the structure of $K_0^*(1430)$.
We calculate the mass and decay constant of $I=1/2$ scalar mesons composed of quark-antiquark pairs based on QCD sum rule. The quauk-antiquark pairs can be $s\bar{q}$ or $q\bar{s}$ ($q=u,d$) in quark model, the quantum numbers of spin and orbital angular momentum are S=1, L=1. We obtain the mass of the ground sate in this channel is $1.410\pm 0.049$GeV. This result favors that $K_{0}^{\ast}(1430)$ is the lowest scalar state of $s\bar{q}$ or $q\bar{s}$. We also predict the first excited scalar resonance of $s\bar{q}$ is larger than 2.0 GeV.
We calculate $D_s^+\to ϕ$ transition form factors $V$, $A_0$, $A_1$ and $A_2$, and study semileptonic decay of $D_s^+\to ϕ\bar{\ell}ν$ based on QCD sum rule method. We compare our results of the ratios of $V(0)/A_1(0)$, $A_2(0)/A_1(0)$, $Γ_L/Γ_T$, and the total decay branching ratio of $D_s^+\to ϕ\bar{\ell}ν$ with experimental data, and find that they are consistent.
We calculate the $B\to P$, $B\to V$ (P: light pseudoscalar meson, V light vector meson) form factors in the large-recoil limit in perturbative QCD approach, including both the vector (axial vector) and tensor operators. In general there are two leading components $ϕ_B$ and $\barϕ_B$ for $B$ meson wave functions. We consider both contributions of them. Sudakov effects ($k_{\perp}$ and threshold resummation) are included to regulate the soft end-point singularity. By choosing the hard scale as the maximum virtualities of internal particles in the hard $b$-quark decay amplitudes, Sudakov factors can effectively suppress the long-distance soft contribution. Hard contribution can be dominant in these approaches.
The two-body nonleptonic charmed meson decays into two pseudoscalar mesons are studied using one-particle-exchange method. The effects of the final state interactions are analyzed through the strong phases extracted from the experimental data.
The study of exclusive B decays in perturbative QCD are complicated by the endpoint problem. In order to perform the perturbative calculation, the Sudakov effects are introduced to regulate the endpoint singularity. We provide a systematic analysis with leading and next-to-leading twist corrections for $B\toπ$ form factors in pQCD approach. The intrinsic transverse momentum dependence of hadronic wave function and threshold resummation effects are included in pQCD approach. There are two leading twist B meson distribution amplitudes (or generally wave functions) in general. The QCD equations of motion provide important constraints on B meson wave functions. The reliability of pQCD approach in \bpi form factors is discussed. 70% of the result comes from the region $α_s(t)/π<0.2$ and 38% comes from the region where the momentum transfer $t\geq 1\GeV$. The conceptual problems of pQCD approach are discussed in brief. Our conclusion is that pQCD approach in the present form cannot provide a precise prediction for \bpi transition form factors.
Again, this preprint has been combined with hep-ph/0207106, which is co-authored by both of us. Therefore, this preprint has been withdrawn. Readers are welcome to refer to hep-ph/0207106.
The pion electromagnetic form factor with leading and next-to-leading twist corrections are studied in the framework of pQCD approach. We find that, at small momentum transfer regions, Sudakov effects cannot provide a strong enough suppression of the non-perturbative contributions coming from large transverse separations, but at large momentum transfer region, non-perturbative contributions can be effectively suppressed. So pQCD approach can be applied at large momentum transfer region. At the energy region where experiment can access so far, i.e. Q < 4GeV, pQCD prediction can not be precise because there may be a quite large part of contributions coming from non-perturbative region. The calculation of power corrections may not be performed systematically in pQCD framework.
We employ one-particle-exchange method to study D-->PV decays in D-->K ρ, πK*, πρprocesses. Taking into account a strong phase and considering nonfactorizable effect, we can get good results consistent with the experimental data. Nonfactorizable effect is not always large, but in some cases, the nonfactorizable effect is nececcesary to accommodate the experimental data. Strong phase is approximately SU(3) flavour symmetric.
We study $D \to ππ$ decays with final state interactions considered in one-particle-exchange method. A clear physical picture for final state interactions based on quark and hadronic level diagrams is presented. A strong phase is introduced for hadronic effective couplings, which is crucial for explaining the experimental data of $D^+\to π^+π^0$, $D^0\to π^+π^-$, and $D^0\to π^0π^0$. Rescattering effects between different $D$ decay channels are usually large. They are important for obtaining correct branching ratios for $D\to ππ$ decays in theoretical calculation.
The end-point singularity is an unsolved problem in BBNS approach. Incorporating the partonic transverse momentum and the Sudakov form factor, this problem can be solved model-independently. We discuss the Sudakov effects in BBNS approach. The BBNS approach is compared with the modified PQCD approach. The main idea of Sudakov form factor is briefly discussed. Our conclusion is that the twist-3 contribution for the hard spectator scattering is numerically not important in $B\to ππ$ decays, compared with the twist-2 contribution.
We calculate the branching ratios and CP asymmetries for $B^0 \to π^+ρ^-$, $B^0 \to ρ^+π^-$, $B^+ \to ρ^+π^0$, $B^+ \to π^+ρ^0$, $B^0 \to π^0ρ^0$, $B^+ \to π^+ω$ and $B^0 \to π^0ω$ decays, in a perturbative QCD approach. In this approach, we calculate non-factorizable and annihilation type contributions, in addition to the usual factorizable contributions. Our result is in agreement with the measured branching ratio of $B^0/\bar B^0 \to π^\pmρ^\mp$, $B^\pm \to π^\pmρ^0$, $π^\pm ω$ by CLEO and BABAR collaboration. We also predict large CP asymmetries in these decays. These channels are useful to determine the CKM angle $ϕ_2$.
We have studied charmless two-body B decays involving $η$ and $η'$ in the framework of QCD improved factorization appraoch. The spectator hard scattering mechanism for $η'$ production have been re-examined and extended, which contributions are incorporated consistently into the factorizable leading contributions. It is found that the conventional mechanism would give $Br(B\to η' K)\sim 30\times 10^{-6}$ which agrees with predictions based on naive factorization approaches. With the incorporation of spectator hard scattering mechanism contributions, theoretical predictions are improved much and the bulk of $Br(B\to η' K)$ are accommodated in the reasonable parameter space. We have also presented calculations of $g^{\ast}g^{\ast}-η^{(\prime)}$ transition form factors within the standard hard scattering approach. It is shown that the new contributions in the modes such as $B\to η' +vector$ and $B\to η+ π, ρ, K^{(\ast)}$ are small. Direct CP-violation in those decay modes are predicted. It is shown that the prospects for measuring direct CP-violation effects in $B^{\pm} \to$ $η' K^{\pm}$, $η' π^{\pm}$, $ηπ^{\pm}$, and $ηK^{\pm}$ are promising at B factories in the near future.
Motivated by recent measurements, we investigate $B\to ππ, K π$ decay modes in the framework of QCD improved factorization, which was recently proposed by Beneke $et al$. We find that all the measured branching ratios are well accommodated in the reasonable parameter space except for $B\to K^0 π^0 $. We also discuss in detail the strong penguin contributions and the ${\cal O}(α_s)$ corrections to the chirally enhanced terms. We find that the weak phase $γ$ lies in the region $120^{\circ}<γ<240^{\circ}$, which is mainly constrained by $B\to π^- π^+ $.
Motivated by recent CELO measurements and the progress of the theory of B decays, we investigate $B\to P V(P=π,K. V= K^{*},ρ,ω)$ decay modes in the framework of QCD improved factorization. We find that all the measured branching ratios are well accommodated in the reasonable parameter space and predictions for the other decay modes are well below the experimental upper limits. We also have calculated CP asymmetries in these decay modes.
We study the $η'-g^*-g$ transition form factor by using the $η'$ wave function constrained by the experimental data on the $η'-γ^*-γ$ transition form factor provided by CLEO and L3 . We also take into account the contribution of the possible gluonic content of the $η'$ meson.