Studies On Transition Form Factors Of B_s To Excited Charmed Mesons

The semileptonic decays of B_s play an important role in testing the standard model of particle physics（SM）,extracting its basic parameters and searching for new physics beyond the SM.At present,the most direct way of extracting the CKM matrix element |V_cb| is through the semileptonic_（）decays into ground state charmed mesons,i.e.B→D（D^*）l（?）.The accura-cy depends on both experimental measurements and theoretical methods for evaluating the non-perturbative effects of strong interactions.Semileptonicdecays into excited charmed mesons constitute the main backgrounds for the measurements of the above processes.Based on the heavy quark symmetry,some model independent predictions for these decays can be obtained.Compared with the traditional heavy quark effective theory（HQET）,the heavy quark effective field theory（HQEFT）is derived directly from QCD and includes the heavy quark-antiquark coupling effects in the finite mass corrections.The non-perturbative contributions can be param-eterized in terms of form factors.In this thesis,we calculate the form factors of B_s decays into P-wave excited charmed mesons D_s^** including D₀^*（2300）、D₁（2430）、D₁（2420）、D₂^-（2460） and their strange counterparts)systematically by using the QCD sum rules in the framework of HQEFT.Firstly,in the theoretical review section,we introduce the relevant research backgounds,theoretical framework and methods involved,including the heavy flavor physics,HQEFT and QCD sum rules.On this basis,we systematically calculate the B_s→D_s^** transition form factors by using the QCD sum rules in HQEFT.We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors,including the scalar and tensor ones form factors only relating to possible new physics effects.It is found that there are some relations among the form factors.Specially,g_-=gT、gV₂=-gT₃、gA=-gT₁=gT₂、f_A=-fT₁=fT₂、k_A2=k_T3·g+is equal to zero in the whole physical region of q² and gp,gv₁,fv₁ approach to zero at q²=q_max².Due to the approximate SU（3）flavor symmetry,the values of B→D^** form factors are very close to their strange counterparts.The uncertainties of form factors come from the free parameters in QCD sum rules,which is about（10-20）%.The results presented in this thiesis can be directly applied to the calculation of observables and theoretical analysis for the relevant exclusive semileptonic decays.