Phenomenological Study Of Two-body Hadronic B_s,b_c Decays With The PQCD Approach

Since the discovery of the bottomonium, such as Υ(1S), Υ(2S),, Υ(5S), B mesonprovides a good place to test the standard model, determine the flavour parameters, explore thesource of CP violation and search for any New Physics signals. Based on the data accumulatedby Babar and Belle, many Buand Bdmeson rare decays have been measured. The large CP-violation efects have been observed in B decays, where sin2β is at the level of3%. But theexperimental study on Bsand Bcmesons is relatively few, due to the fast oscillation of Bsmesonand the tiny yield rate of Bcmeson. With the running of LHC and the advent of SuperKEKB,the amount of Bsand Bcmeson will increase greatly. The potential Bsand Bcmesons allowus to overconstrain or/and overdetermine the parameters extracted from Bu,dmeson decays. Inthis thesis, we will study some Bsand Bcdecays with perturbative QCD approach based on KTfactorization.In the introductory part, the standard model is briefly reviewed, including the elementaryparticles, the electroweak Lagrangian, the quark-mixing CKM matrix, and so on. The low energyefective theory for B weak decays is introduced. The B weak decays are complicated becauseof strong interactions efects at low energy region where the perturbative and nonperturbativecontributions are entangled with each other. There exist a variety of treatments of this problemrelying on assumptions. Some phenomenological treatments, such as the QCD factorization(QCDF) and soft-collinear efective theory (SCET), are explained sketchily. The perturbativeQCD approach (PQCD), which is used by us to study Bsand Bcdecays, is analyzed carefully.The first part of our research is forced on the diferent treatments on the annihilationcontribution. It is believed that the annihilation contribution is power suppressed in the heavyquark limit, and the endpoint divergence must be parameterized with the QCDF approach. It isargued that the endpoint singularity in the annihilation contribution will vanish under the PQCDframework, by retaining the parton transverse momentum and employing the Sudakov factor.The annihilation contributions are calculable with the perturbation theory and can give a largestrong phase. Hence, the pure annihilation decay of Bs→ηc(J/ψ)D is studied with the PQCDapproach, considered three types of Bsmeson wave functions and two types of ηc(J/ψ) mesonwave functions corresponding to the Coulomb and harmonic oscillator potential, respectively. Our estimate shows that the branching ratios for Bs→ηcD, ηcD, J/ψD, J/ψD decays are theorder of107,108,108,109, respectively, where the largest uncertainty is from the wavefunctions. Our results are consistent with the previous estimation on the corresponding U-spinprocess with the same PQCD approach. These decays could be measured in the near future.The other part of our research is forced on the diferent treatments on the form factor andBcdecays. It is argued that the form factor should enter the QCDF factorization formula as anonperturbative quantity, while it is thought that the form factor can be treated completely inthe hard scattering picture with the PQCD approach. The Bcmeson, where both the valenceb and c quark can decay individually, provides a good place to test these two ansatz whichis relative to our understanding on QCD. In our thesis, the form factor Bc→Bqis studiedwith the PQCD approach. It is found that the contribution to form factor comes mainly fromαs/π <0.3region, so it is perturbatively calculable. In addition, the seventeen Bc→BqP,BqV decays are estimated, including the contributions of the tree, penguin, and annihilationoperators. Compared with the tree contribution to the branching ratio, the efects of penguinand annihilation are negligible because they are highly suppressed by the CKM factors. Thereis a hierarchic structure among the bottom conserving and charm changing decay modes Bc→BP, BV, where the color-favored tree decays have large branching ratios. Our estimate onthe Bc→Bsπ decay is agreement with the recent LHCb measurement within uncertainties.Our predictions on the Bc→BP, BV decays provide a ready reference to the existing andforthcoming experiments.At present, several treatments on the hadronic matrix element have been proposed andwidely applied to the B meson decay. There are still some problems which deserve further studyfor these approaches, such as the endpoint divergence, the annihilation contribution, the formfactor, and so on. We hope our research is helpful to experimental and theoretical study onQCD. We also believe that the ongoing experimental program will shed light on these problems.