By The Fourth Generation Quark Model B → Research Kπ Decays

In the filed of high energy physics, B physics has been a hot topic for many years. What’s more, the study of B physics is very important in testing the standard model(SM) and in searching for the signal of new physics beyond the SM. Till now. the B meson experiments, such as those carried out by CLEO、Belle and Babar collaborations, have provided lots of experimental data for the B physics studies. The LHC experiments, specially the LHCb experiment, contribute a lot to B meson physics since they started to run at the end of the year2009.In this paper, we made a systematic study for the four B→Kπ decays in the framework of the SM and the SM with a fourth generation of fermions (SM4), by employing the pertur-bative QCD (pQCD) factorization approach and with the inclusion of the next leading-order (NLO) contributions. In the first chapter, we made a brief review for the history and current situation of the B meson physics, and then we made a short discussion for the problems of the standard model. In the second chapter, we provided a brief introduction for the theoretical framework of two-body charmless B meson decays and the pQCD factorization approach. In chapter three, we presented the outline of the SM4model, and then we made the analytical calculation and found the NLO pQCD predictions for the branching ratios and CP-violating asymmetries of the four B→Kπ decays in the SM. In chapter five, we firstly discussed the effects of the fourth family quarks to the low-energy effective Hamilton and Wilson coeffi-cients then we worked out the branching ratios and CP-violating asymmetries in SM4model. At last, we made a comparison between the pQCD predictions based on the SM and SM4respectively, as well as the latest experimental data. Based on our studies we found that:(1)Due to the inclusion of the NLO contributions, the pQCD predictions for the branch-ing ratios and CP-violating asymmetries of the four B→Kπ decays in the SM become well consistent with the measured values, and therefore we can interpret the so-called " Kπ-puzzle" in the framework of the SM.(2)When the one-loop contributions from the fourth generation t’ quark are taken into account, we found the stringent limit on the free parameter mt’ of the SM4by phenomeno-logical analysis, mt’=[600,920]GeV. The(?)s dependence of the SM4predictions is complex and it is difficult to find a simple limit on the value of (?)s.