Studies On Exclusive Semileptonic Decays Of B_（s） To （3/2）⁺ Excited Charmed Mesons

In recent years,studies on the B_（s）to excited charmed meson semileptonic decays receive much attention both theoretically and experimentally.Semileptonic B_（s）decays into excited charmed mesons contain the main background for measuring the corresponding decays into ground states.To get precision knowledge on the branching fractions of B_（s）decays into ground states,extract the CKM matrix element |V_cb| and resolve the problem of R（D（*））anomalies,reliable measurements and calculations on the semileptonic decays into excited charmed mesons are needed.The four lightest excited charmed mesons D₀^*（2300）,D₁（2430）,D₁（2420）,D₂^*（2460）and their counterparts of cs states D_s0^*（2317）,Ds1（2460）,D_s1（2536）,D_s2^*（2573）come in degenerate doublets with jlP=3/2+ and jlP=1/2+ in the heavy quark limit.In the present thesis,we aim to investigate the semileptonic B_（s）decays into 3/2+ excited charmed mesons D₂^*（2460）,D_s2^*（2573）,to the next leading order of heavy quark expansion in the framework of heavy quark effective field theory（HQEFT）,calculating the relevant form factors and predicting the bin-averaged values for the longitudinal polarization fraction,CP averaged forwardbackward asymmetry and angular asymmetries in different kinematical bins.Firstly,we give a brief review of the standard model of particle physics（SM）and the current status of theoretical investigations on the semileptonic B_（s）decays into excited charmed mesons.On this basis,we calculate the B_（s）→D₂^*（2460）、D_s2^*（2573）form factors by using the QCD sum rules,to the next leading order of heavy quark expansion in HQEFT.With the form factor results,we investigate the relevant semileptonic decays B_（s）→D2*（s2）lv,calculating the bin averaged values for the longitudinal polarization fraction FL,CP averaged forward-backward asymmetry AFB,CP averaged asymmetry A3 and angular asymmetries A4（5）in different kinematical bins.It is found that the bin-averaged values of observables for the Bs→Ds2*lv decays are slightly smaller than the results for the B→D₂^*lv modes.The uncertainties come from the free parameters ωc*,ωc*（1）and T in the calculations of form factors.The large uncertainties of the universal wave function τ,η0b（c）induced by the free parameters have little effect on the bin-averaged values for observables.Therefore,the uncertainties of the bin-averaged values for observables given by us is extremely small,basically zero under the numerical accuracy considered.The bin-averaged values for the longitudinal polarization fraction（）decrease with the increase of the momentum transferred squared（q~2）.For the decays with μ in the final states,the bin-averaged values for the forward-backward asymmetry(is positive,increase first and then decrease with the increase of q~2.For the decays with τ,the results ofincrease with the increase of q~2 and its sign changes from negative to positive.These results can be tested by more accurate experiments in the future.