Phenomenological Study Of Y(nS) And B~* Meson Semileptonic Weak Decays

Particle physics is the study of the microscopic structure of matter and its dynamics. At present, in particle physics, the Standard Model(SM) is the most successful theory for describing the elementary particles and their strong, weak and electromagnetic interactions. But in many ways, it is not enough, it is an effective theory at low scale rather than an ultimate theory. Heavy flavor physics, such as the b physics plays an important role in testing the flavor dynamics of Standard Model(SM), exploring the source of CP violation, searching the indirect hints of new physics and investigating the underling mechanisms of QCD et al. In the (b(?)) bound state, between the ground state (?)q* vector meson decays and the bound state (?)q meson decays,there are many similarities and correlations,which provide a broader space for testing the Standard Model and probe possible hints of new physics (NP).This paper firstly introduces the basic content of the Standard Model, including the elementary particles , Lagrangian and CKM matrix in the Standard Model, etc. Then some important theoretical tools are reviewed, including the calculation of the hadron matrix elements, renormalization and renormalization group, etc. Finally, we introduce our research work, mainly in the following two parts:(i)Study of semileptonic (?)*u,d,s?Pl-*l decays. In anticipation of abundant (?)* data samples athigh-luminosity heavy-flavor experiments in the future, the tree-dominated semileptonic (?)*u,d,s?Pl-(?)l(P=D, Ds,?,K)decays are studied within the Standard Model. After a detailed calculation of the helicity amplitudes, the theoretical predictions for branching fraction (decay rate), lepton spin asymmetry,forward-backward asymmetry and ratio RD*(L) are firstly presented. It is found that the tree-dominated (?)*?Dl(?)l decays have relatively large branching fractions of O(10-9)?O(10-7),and are in the scope of running LHC and forthcoming SuperKEKB/Belle-? experiments, therefore this decay is expected to be observed in the future experiment.(ii)Study of Semileptonic Y(nS)?Bcl(?)l weak decays. In this paper, the tree-dominated and CKM-favored Y(nS)?Bcl(?)l (n = 1,2,3) decays are studied within the Standard Model. This decay process is similar to (?)*?Dl(?)l decays, which is caused by b?cl(?)l transition at the quark level. The theoretical predictions and some discussions for the observables including the branching fractions, the ratios RY(nS),the lepton spin asymmetries and the forward-backward asymmetries are presented.Numerically, the Y(nS)?Bcl(?)l decays have relatively large branching fractions of the order O(10-10)?O(10-9). In addition, the feasibility of measuring these decay modes at the current heavy-flavor experiments(LHCb, CMS, Belle-II) are discussed.