Rare Decay And New Physics Effects In B Meson

The Standard Model (SM) of particle physics is a gauge theory concerning the fundamental interactions between elementary particles. The development of the SM was driven by various theoretical and experimental tests over the latter half of 20th century. Although successful in explaining a large variety of experimental results, it does leave some phenomena unexplained and still falls short of being a complete theory. The study of searching for New Physics(NP) be-yond the SM has become one of the most significant tasks in high energy physics. Heavy flavor physics, especially B physics, has been playing an important role in testing the SM, searching forNP.In this thesis, we have performed detailed phenomenological analysis of the widely dis-cussed B-meson decays. The structure of this thesis has been organized as follows, we give a brief summary of the SM and the related theoretical tools of dealing with the calculations in B-meson decay process, including the operator product expansion, renormalization group equa-tion. The relevant low energy effective Hamiltonian is also provided. After that, we will review the schemes used to calculate the hadronic matrix element with the emphasis on the application of QCD factorization in two-body semi-inclusive decay. Finally, we present the main body of this thesis, consisted of two parts:Part â… , we study the Bâ†'η(t)Xs process within the framework of the SM, with contri-butions from bâ†'η(t) s and b â†'η(t)sg simultaneously considered. In the two-body decay mechanism, we calculate the branching ratio of this process in naive factorization approach and QCD factorization approach, respectively. By introducing ACCMM model, we obtain the re-coiling invariant mass distribution of Xs. The three-body decay mechanism bâ†'η’sg has been cooked with the contribution from the coupling of η(t)g*g which is computed in the standard hard scattering approach (HSA), the Feynman diagrams considering the gluon radiated from an external quark,the outgoing meson or internal fermion loop together with the bremsstrahlung gluon of the strong penguin. With both the two-body decay mechanism and the three-body de-cay mechanism taken into account, the branching ratio of B â†'ηXs is found to be consistent with the experiments, while that for B â†'η’Xs is too small compared to the measured results.Besides the framework of the SM, we can also employ the well measured decay process sensitive to NP to provide additional constraint on the allowed parameter space for NP beyond the SM. This leads us to the second part of the major work in this thesis.Part â…¡, we can give the parameter space constraint on the top quark tcZ anomaly coupling with the recent experimental results on Bâ†'K*μ+μ- and Bs â†'μ+μ-. For the top quark flavor-changing neutral current t â†' qZ, the branching ratio is predicted to be around 10-10 in the SM, far below the detectable experimental precision. However, this process is supposed to be enhanced significantly in the models containing NP. Any positive experimental signal for this process can be thereof considered as the supportive evidence for NP. Except for the direct search of tâ†'qZ decay on high energy colliders, we can also study the effect of the anomalous coupling on top quark loop at low energy, We carry out systematical studies on the anomalous tcZ coupling in Bâ†'K*μ+μ- and Bsâ†'μ+μ-.With the constraint from experiments on these two channels, we find that the obtained upper limit for B(tâ†'cZ) is at the same level of the direct measurement result from CMS for complex anomalous coupling, whereas lower than the current CMS results for real anomalous coupling, but still in the accessible level of LHC in the High-Luminosity run.