Studies On Two-body Charmless Hadronic B_c Meson Decays In The Perturbative QCD Approach

In 1998, the first observation of approximate 20 Bc events in the Bc?J/?(?) decay mode was made by the CDF collaboration. The Large Hadron Collider(LHC) at CERN is running now. Around 5×1010 Bc meson events are expected to be produced in the LHC experiment per year. Rather different from the light Bq(q= u,d,s) mesons, the Bc meson looks more special due to the fact that she embraces two different heavy flavor c and b quarks simultaneously. Studies on the hadronic Bc meson decays can help one to test the standard model(SM) and investigate heavy flavor physics better; on the other hand, they can provide a new realm for experimental measurements to explore the hadronic QCD dynamics in the final states. Furthermore, the pure annihilation nonleptonic Bc decays may provide the golden grounds for studying the annihilation contributions and could offer the important clues to understand the size, even the corresponding mechanism of weak annihilation contributions in the decays of light Bq mesons comprehensively. The studies on the hadronic Bc meson decays are therefore very important for the development of particle physics.As is well known that the effective evaluation of hadronic matrix element is always the difficult task and the key point in studying this kind of decays. Up to now, many factorization approaches have been proposed and used in studying the B meson decays, such as the QCD factorization approach(QCDF), the soft-collinear effective theory(SCET) and the perturbative QCD(pQCD) factorization approach. They can phenomenologically provide the theoretical predictions about many physical observables, which are basically consistent with those measured by the experiments. Particularly, the pQCD factorization approach highly succeeds in the theoretical investigations on the magnitudes of annihilation contributions. In this thesis, the author made the systematic studies on the two-body charmless hadronic Bc meson decays, specifically those pure annihilation decay modes, by employing the pQCD factorization approach, and found many interesting and important results.In the first two chapters, starting with the light meson spectroscopy, the author pre-sented a review about the status and perspective of the p-wave light-quark mesons, and the Bc meson physics in the LHC experiments. respectively. The six major factorization methods and/or approaches being used by many authors to calculate the hadronic matrix element are comparatively introduced. While the pQCD factorization approach adopted in this thesis is expatiated with emphasis, for example, the introduction of the transverse momentum kT, smearing the end-point singularity, and the Sudakov form factor, etc. Some recent progress/developments of the pQCD factorization approach, such as the treatment of Glauber gluons, are also discussed. Moreover, the essential discussions on the wave functions describing the nonperturbative behavior of the hadrons are also given.In the third to fifth chapter, the author made a systematic theoretical investigations and a phenomenological analysis on the physical observables, such as the CP-averaged branching ratios, the polarization fractions and/or the relative phases, for the 186 considered pure an-nihilation decays:Bc?PP,PV,VV, Bc?SP,SV, and Bc?AP,AV, AA, by employing the pQCD factorization approach in the SM, and found the following results:(1) The theoretical predictions of branching ratios for all 186 decay channels are varying in the range of 10-9?10-5. Our theoretical predictions for the modes such as Bc?(?) K(*)+ are basically consistent with those obtained in the SU(3) flavor symmetry. The decay rates with 10-6 or larger will be measured with good precision at LHC experiments, which can offer the great opportunities to study the structure of the heavy Bc meson and test the reliability of the pQCD factorization approach adopted in this thesis;(2) Those decays with a branching ratio at the level of 10-7 or below are hardly to be measured in the LHC experiments. However, once they were observed, a window will be opened to study the involved nonperturbative QCD dynamics or final state interactions, even new physics beyond the SM;(3) Among the considered channels, the branching ratios of the?S= 0 modes are generally much larger than those of the?S= 1 ones, just the situation as being expected. The main reason is that the former has a large CKM factor (Vud?1) while the latter has a strongly suppressed CKM factor (Vus?0.22). Since there are only contributions arising from tree topology, the CP-violating asymmetry vanishes naturally because of the absence of the weak phases in the SM for these charmless hadronic Bc meson decays;(4) In the decay channels with polarization states, most of them are dominated by the longitudinal contributions. It is expected that the ongoing LHC and forthcoming Su-perB experiments can provide some insights to further understand the helicity contents involved in these types of decay modes;(5) When enough Bc meson events are available, they can provide the fertile soil for studying the hadronic dynamics involved in the final states of those decays, and provide dynamical evidences for conjecturing the internal structures of the light scalars and axial-vector mesons and investigating their physical properties;(6) Comparing with Bu meson, the branching ratios of annihilated Bc meson decays can get the enhancement of a factor |Vcb/Vub|2?100, which will put up more evi-dences for the studies on annihilation decays, and establish a solid foundation for bet-ter understanding the size, even the corresponding mechanism of the weak annihilation contributions occurring in the decays of the light Bq mesons.In the last chapter, a short summary of the thesis and some remarks on the perspectives of the heavy b flavor physics in the forthcoming years are given.