Studies Of Some Semileptonic And Hadronic Decays Of B Meson

B meson physics is the very important area in current theoretical and experimental studies of high energy physics. The three main objectives of the B meson physics are:(a) the precision test for the standard model (SM);(b) the precision measurements for the CP-violating asymmetries of b meson system (B, BSO and Bc) and for the flavor parameters; and (c) the search for the signal or any evidence of the new physics beyond SM. In the summer of1999, the two B factory experiments, BaBar and Belle, began their running. When Belle collaboration finally stop running at June of2010, BaBar and Belle collaborations together collected about1.7x109pair production and decay events of B meson. They found the CP violation of B meson system, measured several hundred decay modes of B meson, and also observed many exotic states X, Y and Z. The two B factory experiments are indeed making a great success, and the theoretical studies of B meson physics also made remarkable progresses simultaneously. Since its running at the November of2009, the LHC experiments, especially the LHCb collaboration, have accumulated a large amount of B/Bs/Bc meson events. At the July4th of2012, the ATLAS and CMS collaborations announced the discovery of the "Golden particle":the Higgs boson after half century’s efforts to find it, a dream finally becomes a real! They also made great contributions to the heavy flavor physics. The super-B factory at Japan, furthermore, will begin to run around2015, and could provide a huge data sample, about two orders higher than we have now. We therefore believe that a new "Golden Era" of B physics is coming near after great success in the past decade.In this thesis, we have made systematic studies for the two body charmless hadronic decays Bâ†'Kη(’) and the semileptonic decays of B/Bsâ†'D(s)(*)lvl, by employing the per-turbative QCD (pQCD) factorization approach based on the kT factorization theorem.In the review section of this thesis, the author makes a brief review about the standard model and the basics of the heavy flavor physics, presents an introduction for the current status of theoretical studies and experimental measurements. We focus on the discussions on the CP violation of B meson system, as well as the popular factorization approaches being used in the calculation of the matrix elements of hadronic transitions, specially the pQCD factorization approach and its latest developments.In the third and the fourth chapters, we will show our main works completed very recently. In the third chapter, the author makes a system study on the two body hadronic charmless decays Bâ†'Kη(’),focusing on the evaluation for the effects of the next-to-leading order (NLO) contributions from various sources. By considering the three differentη-η’mixing schemes, we make a systematic study for Bâ†'Kη(’) decays, calculate the branching ratios and CP-violating asymmetries and compare the relative strength of the contributions from different sources and at different orders. From the numerical results and phenomenological analysis, we find the following points:(1) For the three kinds of mixing schemes being used in our work, the NLO pQCD predic-tions for the branching ratios and CP-violating asymmetries agree well with the data within one standard deviation. By using the η-η’-G mixing scheme, specifically, one can provides a very good interpretation for the measured values. The NLO contribu-tions produce rather different effects to the different decay modes, but all lead to some improvements for the consistency between the pQCD predictions and the data.(2) The inclusion of the NLO contributions to the form factors of Bâ†'K transition can produce an～20%enhancement to the branching ratio Br(Bâ†'Kη(’)), which helps one to explain the large observed branching ratio Br(Bâ†'Kη(’)).(3) After the inclusion of the NLO contributions, the agreement between the pQCD predic-tions of the CP-violating asymmetries of Br(Bâ†'Kη(’).decays and the data is improved effectively.(4) The factorizable emission diagrams provide the dominant contribution to the considered decays, the contribution of the spectator diagrams is small. The real part of the annihilation diagrams in general is very small, but their imaginary part is relatively large and leads to a large strong phase, which explains the relatively large CP violation as reported by the experiments. (5) According to this study, we believe that those still missing NLO corrections of the spectator diagrams and the annihilation diagrams are the high order corrections to the small quantities, its size is smaller than the error of the experimental measurements, and therefore can be neglected safely.In the forth chapter, we make a system study for the current "hot topic"-B/Bsâ†'D(s)(*)lvl semileptonic decays in the framework of the SM by employing the pQCD factorization approach. Based on our estimation for the relevant form factors and the numerical results, we find the following points:(1) The pQCD predictions for the branching ratios of Bâ†'D(s)(*)l-vl and Bsâ†'D(s)(*)+l-vl decays agree well with other predictions based on different methods in the SM and the measured values within one standard deviation. For the isospin-constrained ratios R(D) and R(D*), the pQCD predictions agree well with the BaBar measurements and provide an interpretation for the BaBar’s anomaly in the framework of the SM. For the newly defined ratios RιD and RÏ„D, which may be more sensitive to the QCD dynamics of the considered semileptonic decays, therefore, we suggest to measure them in the forthcoming experiments.(2) For the BsOâ†'D(s)(*)lvl semileptonic decays, we defined four new ratios of the branching ratios:R(Ds(*) and RDsι,Ï„, to be tested in the future experiments.(3) The pQCD predictions do support the SU(3)F flavor symmetry between Bsâ†'D(s)(*)+l-vl and Bâ†'D(*)l-vl decay modes. Our calculations show that:the break-ing of SU(3)F flavor symmetry is around10%.In the fifth chapter, the author gives a simple summary for the thesis, and makes some discussions and the prospects for the future developments of the B meson physics. With the steady progress in the calculations of higher order corrections, the reliability and the accuracy of the pQCD factorization approach will be improved continuously. We do wish our theoretical predictions be tested by the forthcoming experimental measurements.