B_d,s⁰→f₁f₁ Decays With F₁（1285）-f₁（1420）Mixing In The Perturbative QCD Approach

The studies on nonleptonic B meson decays can provide a good place to examine the standard model and can also offer an effective method to explore the possible new physics.The experimental apparatus in specialty for B physics,such as BABAR,Belle(-Ⅱ),and LHCb,could strongly help investigate the B meson decays.Currently,many axial-vector mesons have been observed experimentally,but with unknown nonperturbative dynamics,for example,the inner structure,which demands more studies and explanations theoretically.Therefore,it is expected that the studies on the two-body B meson decaying into the final states involving axial-vector mesons could provide evidences and references indirectly for the experimental measurements.In the review part of this thesis,i.e.,the first two chapters,the author mainly introduces the basic theory of B meson physics and the perturbative QCD(PQCD)approach.And the basic idea and the advantages of the PQCD approach are presented explicitly.In the third and fourth chapters,the author calculates the Bd,s0→f1f1 decays by employing the PQCD approach,in which the Bs0→f1f1 modes are studied for the first time in the literature.Based on the available measurements,the mixing angle φf1 is taken as 24°.Then,the author evaluates numerically the measurable observables such as the branch ratios,the polarization fractions and the direct CP violations,and so forth.By combining various results and phenomenological analyses,some conclusions could be obtained as follows:(1)The almost pure penguin modes Bs0→f1f1 have large branching ratios in the order of 10-6～10-5 due to the Cabibbo-Kobayashi-Maskawa enhancement and generally constructive interferences between the amplitudes of Bs0→fnfs and Bs0→fsfs with fn and fs being the quark-flavor states of f1 mesons.(2)The observables receive important contributions from the weak annihilation diagrams in the PQCD approach.In particular,without the annihilation contributions,the Bs0→f1(1420)f1(1420)branching ratio will decrease about 81%and its longitudinal polarization fraction will reduce around 43%.(3)The dependence of the Bd,s0→f1f1 decay rates on φf1 exhibits some interesting line shapes,whose confirmations would be helpful to constrain the determination of φf1 inversely.Finally,the author summarizes this thesis briefly and makes an outlook for the prospects of B physics necessarily.