Phenomenological Studies Of B → S Transition And Possible New Physics

The Standard Model (SM) of elementary particles is a theory based on the gauge group,which purports to describe the strong and electroweak interactions of fundamental parti-cles. Until now, it is the best theory for describing the dynamics of fundamental particles.However, the SM itself is not perfect, because there are also some problems that haven'tbeen solved reasonably yet, which indicates that the SM is not an ultimate theory but ane?ective theory at low scale. It provides room for developing new physics (NP) beyondthe SM, i.e. at the higher energy scale, there should exit some new and more basic theory.Heavy flavor physics, especially B physics, is a perfect region for testing SM, pursuingthe origin of the CP violation and searching for possible NP. Accordingly, the study ofB-meson decays is one of the currently very active researching fields.In this thesis, we focus on some current very interesting puzzles in B meson decaysand pursue possible solutions with NP e?ects. Firstly, we briely introduce SM and somebasic concepts, including the CKM matrix, unitarity triangle, renormalization group andso on. Secondly, we review the low-energy e?ctive Hamiltonian relevant to B-mesondecays and various aspects of the QCD factorization approach. Finally, we present themain body of the thesis, which is composed of the following parts:Firstly, within the QCD factorization framework, for B→PPˉPV processes, wequote a new infrared finite gluon propagator as an alternative to regulate the end-pointdivergency, which exist in the hard spectator corrections and annihilation contributins.In this part, we focus on the e?ects of such new scheme on the strength and strongphase in hard spectator corrections and annihilation contributions. Combining the up-to-date experiment measurment for B→πK,Ï€K^*andρK decays, within the QCDfactorization framework, we analyze the existing"Ï€K puzzle". We introduce a group ofmodel independent (pseudo-)scalar operators (?)(1 +γ₅)b(?)(?)(1 +γ₅)q (q=u,d) for possiblesolution. Our numerical results show that, within the allowed NP parameter space, all of the obsevables of the twelve decays agree with the experimental data which implies thatthe"Ï€K puzzle"coulde be resolved with the contribution of (peudo-)scalar operators.After introducing a family nonuniversal Z' model in detail, we revisit the"Ï€K puzzle"for possible solution within such a model. With the up-to-date experimental data, weperform a fit on the Z' couplings in five different cases. Our fitting results indicate thata new weak phase-86°, which is relevant to b-s-Z'coupling, is crucial to the obseved"Ï€K puzzle".B_s-(?)_s mixing, B_s→μ⁺μ^-and B→X_sμ⁺μ^-decays, which also involve b→s transition, are sensitive to NP effects. Recently, both CDF and D0 collaborationsannounced a new CP violation evidence in B_s system. With the fitting results for afamily nonuniversal Z' couplings in B→πK,Ï€K^*andρK decays, We study their effectson B_s-(?)_s mixing, B_s→μ⁺μ^-and B→X_sμ⁺μ^- decays, and get a more accurateb-s-Z'andμ-μ-Z' couplings than the previous works. We find the discrepancybetween the SM prediction and experimental measurment of B_s-(?)_s mixing could bebridged by Z' contribution without violating the bounds from the other decays. Motivatedby the observed mismatches between the SM prediction and experimental measurmentfor the forward-backward in B→K^* decay, which involvs b→s transion also, weperform a further analysis for a family nonuniversal Z' couplings'effects. We find theforward-backward in B→K^*μμdecay could be enhanced about 80%(50%)by Z'contributions at low q² regions in the allowed new coupling space. However, due to thestrong constaints from B→X_sμ⁺μ^- on theμ-μ-Z' coupling, such result also can'tagree with the experimental data within 1σerror.Besides B-meson system, some decays such asÏ€,η→ι⁺ι^-, which have been measuredexactly, also provide a fertile ground for testing SM and possbile NP. Recently, HyperCPCollaboration has observed three events for the decayΣ+→pμ⁺μ^-with a narrow rangeof dimuon masses, which may indicate that the decay proceeds via a neutral intermediatestate,Σ+→pP⁰, P⁰→μ⁺μ^-, with a P⁰ mass of 214.3±0.5MeV. This particle is treated as a candidate of the light CP-odd Higgs A₁⁰ in next-to-mimimal supersymmetricstandrd model (NMSSM). CombiningÏ€⁰→e⁺e^-,γγ,Υ→γA⁰₁ decays with a_μ, weperform a constraint on the light CP-odd Higgs A⁰₁ and find that below 7.8GeV there isnot a suitable new pseudoscalar to fulfill the constraints. Moreover, the branching ratioproblem inÏ€⁰→e⁺e^- decays also can't be resolved within NMSSM.