| The weak decay of heavy mesons is one of the important entry points for studying the properties of elementary particles.Weak decays are mainly divided into semi-leptonic decays with leptons in the final state,pure-leptonic decays non-leptonic decays and nonleptonic decays.The relativistic effect is significant in the weak decay of heavy mesons,and its influence cannot be ignored.Therefore,the method of relativistic covariance is needed to study it in theoretical research.With the accumulation of data in B factory,experimental data related to heavy meson decay is also increasing rapidly,and the accuracy requirements for heavy meson theoretical predictions are also increasing.Therefore,a theoretical method that can fully consider the relativistic effect is also very important for verifying the experimental results.Accurate calculation of the form factor is a prerequisite for calculating many physical quantities in the heavy meson decay,because it directly reflects the magnitude of the decay amplitude.In order to accurately calculate the form factor,we propose an improved Bethe-Salpeter method(improved BS method).Different from the original BS method,the improved BS method discards some assumptions that destroy the relativistic covariance.While retaining the advantages of the original BS method,it becomes a method for calculating the form factor that is more in line with the requirements of the relativistic covariance.We used the improved BS method to calculate the form factor of the B meson decay channel.Finally,we compared the obtained results with the original method and experimental measurements to confirm the reliability of the new method.At present,the theoretical calculation values of R(D),R(D*)and R(J/ψ)deviate from the experimental values,especially the latest experiment of R(J/ψ)The deviation between the value and the theoretical prediction value is relatively large.In order to accurately calculate the values of R(D),R(D*)and R(J/ψ),we use an improved BS method to calculate the semi-leptonic decay of Bq(q=u,d,s,c)mesons.Then we give the calculated values of R(D),R(D*)and R(J/ψ),and compare them with experimental results and other methods.We also calculated the observable measures of the semileptonic decay of the heavy meson containing b quark,such as the differential decay width spectrum,the front and back asymmetry and the lepton polarization asymmetry,and gave the corresponding changes.The semi-leptonic decay and non-leptonic decay of B,Bs and Bc meson to the radially excited state heavy meson are calculated using the improved BS method and QCD factorization.The final states selected are mainly 2S and 3S state.The branching ratios of the non-leptonic decay modes of these decay channels are calculated.And the ratios of the branching ratios of some of the decay channels are compared with the existing experimental values to judge the reliability of the calculation results.The branching ratio of the non-leptonic decay whose final state is an excited state is calculated,and the decay channels,which could be detected is given.The processes of Bc meson decay to two heavy mesons are studied:Bc→cc(2S,2P)+cq(1S,1P),Bc cc(1S)+cq(2S,2P),Bccc(1P)+cq(2S),Bc cc(1D)+cq(1S,1P)and Bc→cc(3S)+cq(1S)(q=u,s).For these decay channels where the final state is two heavy mesons,CP violation is a very worthwhile quantity to study.Using a scheme combining simple factorization and improved BS method,the branching ratio and CP violation value of the selected decay channels are calculated.The decay channels which are most likely to be detected experimentally are determined.The influences of CKM phase angle,mixing angle,gluon momentum,factorization,and final state interaction on the calculation results are discussed. |
