Perturbative QCD Approach And B Meson Quasi-two-body Decay Study

Since the development of the Standard Model,testing the Standard Model has taken on significant significance in particle physics.People are frantically looking for proof of the existence of novel physics because the Standard Model is unable to fully explain all the events observed in experiments.The study of B mesons is an important avenue for searching for new physics,and has received widespread attention from researchers.In terms of experiments,groups such as BaBar,Belle,and LHCb have observed a large number of B meson decay events,providing excellent testing grounds for theoretical research.In terms of theory,researchers have developed many methods to study B meson decay,with the perturbative QCD factorization method being one of the main methods for theoretical calculations of B meson decay.The main focus of this article is on the theoretical calculation of B meson three-body decay using the framework of the perturbative QCD method.If we directly calculate the B meson three-body decay from the hard-core evolution of the b quark decay,it would involve hundreds of Feynman diagrams at the leading-order level,including two virtual gluons.This makes the calculation extremely complex.However,in reality,the momentum region where both hard gluons are exchanged in B meson three-body decay is suppressed by powers of momentum,and their contribution is not important.In particular,when two mesons in the final state come from the same intermediate resonance,the dynamics associated with these two mesons can be factorized into the two-meson wave function.By introducing the two-meson wave function,we can treat this type of three-body decay as a quasi-two-body decay.Since the non-perturbative input-the off-shell shape factor contained in the two-meson wave function-is a function of the invariant mass of the two mesons in the final state,the resulting branching ratio is a differential spectral distribution with respect to the invariant mass of the two mesons.The first part of this paper is the introduction,which presents the development status of particle physics and heavy flavor physics.In Chapter 2,the relevant theory of B meson decay is introduced,including the effective low-energy Hamiltonian,methods for calculating hadronic matrix elements,and meson wave functions.Chapter 3 introduces the theoretical framework of pQCD method,including factorization theorem,kT factorization,Sudakov factor,and threshold resummation,etc.Chapters 4 and 5 describe the application of pQCD method in handling quasi-two-body decays.Chapter 4 examines the use of the pQCD method in the B meson decay channel B→K*γ→Kπγ,and Chapter 5 discusses the use of the pQCD method in the Bc→D*P→DπP channel.We get to certain conclusions in these two chapters.(1)Under the conditions of narrow width approximation and isospin conservation,the branching ratio of our calculated quasi-two-body B meson decay B(s)→K*γ→Kπγ is the same as that of the two-body B decay previously calculated by the pQCD method results agree with the previous results of branching ratio of two-body B decay B(s)→K*γ and are closer to the experimentally measured data.(2)The direct CP breakage of Bu,d→K*γ→Kπγ decays caused by b→s jumps was calculated,and their direct CP breakage is small,less than 1%.If in the future it is confirmed that the direct CP breaking will exceed a few percent,it can be assumed that there exists some new physics contributing to these decay channels.(3)The direct CP breaking of the BS→Kπγ decay caused by the b→d jump is calculated and relatively large direct CP breaking is observed,which can be verified in the LHCb and Belle Ⅱ experiments.(4)The branching ratio of the quasi-two-body BC+→D*+P→D0π+P decay has a clear hierarchical relationship Br(BC+→D*+K0→D0π+K0)>Br(BC+→D*+π0→D0π+π0)>Br(BC+→D*+k0→D0π+η(’)),where Br(BC+→D*+k0→D0π+k0)is the largest,in the order of 10-6.It can be observed experimentally by LHCb.(5)The branching ratio of the)BC+→D*+η→D0π+η decay channel is larger than that of the BC+→D*+η’→D0π+η’ decay channel.It is composed of A(BC+→D*+ηq→D0π+ηq)and A(BC+→D*+ηs→D0π+ηs)caused by the opposite interference between these two amplitudes.(6)For the quasi-two-body BC+→D*+P→D0π+P decay,from the D0π+ invariant mass dependence of these associated decay spectra,we can find that the main part of the branching fraction is concentrated in a very small region near the extreme mass of D*+.Finally,the whole paper is summarized and an outlook for the future is given.