Hqet and Semileptonic Form Factors

Theoretical approaches to form factors of semileptonic decays are discussed in application to B → D + l + ν̄l decay. HQET AND SEMILEPTONIC FORM FACTORS ARKADY VAINSHTEIN Theoretical Physics Institute, University of Minnesota and Budker Institute of Nuclear Physics, Novosibirsk Theoretical approaches to form factors of semileptonic decays are discussed in application to B → D + l + ν̄l decay. 1 Outline Heavy Quark Effective Theory (HQET) 1 is a powerful approach to the processes involving heavy flavor hadrons and, in particular, to the study of form factors of semileptonic decays (see reviews ). From a field-theoretical standpoint, the HQET is a particular example of construction based on a more general notion of Wilson Operator Product Expansion (OPE) or Wilson effective action , to which I mainly refer. The outline of the talk is as follows: • Heavy flavor decays as short distance probes. Total semileptonic widths • From inclusive to exclusive: bounds for B → D∗ leading form factor • Subleading B → D∗ form factors • Some recent developments • Conclusions 2 Heavy Flavor Decays as Short Distance Probes The quark picture of semileptonic B meson decay B → D+ e+ ν̄e is presented by Fig. 1. (Better to put B̄ but I will systematically neglect by bar on B.) The specific feature of heavy flavor states is that they contain a heavy quark Q which could be viewed as an almost static object (in the rest frame of hadron). Thus these states can be considered as ground states of light flavor QCD in the presence of static source of gluon filed. A relevant theoretical parameter is ΛQCD mQ ≪ 1 . (1)