Form Factors In PQCD Based On The K_T Factorization Theorem

As a research area involving effective Hamiltonian and the QCD factorization,the B meson physics,which plays an important role for precision test of the Standard Model(SM)and the search for the possible signals of the new physics,is one of the hot topics for both theoretical and experimental studies of the heavy flavor physics.Since many energy scales are involved in B meson decays,the method of operator product expansion(OPE)and the factorization theorems must be used to make predictions.By applying OPE and integrating out heavy gauge bosons(W±,Z0)and top quark propagators,the effective Hamiltonian can be obtained.The Wilson coefficients can be extracted by matching the full amplitudes with those effective ones,then the hadronic matrix elements can be cal-culated by applying factorization theorems.The perturbative QCD(PQCD)approach based on the kT factorization theorem is one of the major factorization approaches to evaluate the hadronic matrix elements.In PQCD approach,to avoid the endpoint singu-larity,the transversal momentum kT is taken into account in the end point region.The double logs generated by the radiation corrections can be resumed into the so called Su-dakov factor,which can further suppress the large transverse separation area and ensure the validity of the perturbative calculation in typical scales.In the framework of the PQCD approach,people have studied systematically many decay modes of B mesons at the full leading order(LO)level,and the major parts of the next-to-leading order(NLO)corrections have also been completed.Meanwhile,to explain the anomalies appeared in recent years in B meson experiments,it is necessary to improve the precision and the credibility of the theoretical calculations.The NLO and even NNLO corrections should be calculated to support the analysis of the experimental date.In this paper,we try to extend the previous studies at the LO to the NLO level for some typical decay modes of B mesons.In PQCD approach based on the kT factorization theorem,we study the factorization for the ??*?? and B ?lv transitions.Then we extend the factorization to exclusive processes of the light vector meson and B?V decay modes.The chapter 2 and 3 are the review parts of this paper.In chapter 2,we simply introduce the basic contents of the SM and the effective theory of the weak interactions.In chapter 3,the factorization theorem,both the collinear factorization and the kT factorization,is introduced in details.The chapter 4 and 5 contain my own work,we extend the factorization of ???(?)and B?? to the NLO level,and calculate the NLO corrections to the form factors of ???and ???.The main results are as follows:(1)In ??? transition process,the LO contribution involves three combinations of different twists,and the term proportional to ??T(x1)??P(x2)provides the dominate contribution(about 80%).We focus on the calculation for the NLO corrections to the dominate channel,and find that the resultant NLO correction can provide about 20%enhancement to the LO form factor.Also,by analytic continuation,we derived the time-like from factors for ??? transition with the inclusion of the NLO corrections.The NLO corrections of the time-like from factors are relatively large but still under control.For the case of ??? transition,we calculate several combinations of twists which may contribute to form factor in LO,then three dom-inate channels are discovered.The NLO corrections to these channels manifest that the NLO contributions provide about 30%enhancement to the LO form factor in typical energy scale.Such magnitude of the NLO corrections agrees with the general expectation.(2)We make the factorization proof for B?p transition process at the NLO level,and give the non-local matrix elements of the distribution amplitude.For B?V cases,in general,soft divergence cannot be cancelled completely,those remaining divergence will be absorbed into the jet function and the meson wave functions.Now the calculations for the NLO corrections to the form factors in PQCD factor-ization approach are partly completed,while many issues should be resolved to complete the whole work.Any advances in this field will be a help to improve and develop the PQCD factorization approach itself,and also mean a better support to the analysis of the experimental measurements.