WEAK MATRIX ELEMENTS AND |Vcb| IN HQEFT

Abstract

The heavy quark effective field theory (HQEFT) containing both effective "quark fields" and "antiquark fields" is investigated in detail. By integrating out (but not neglecting) the effective antiquark fields, we present a new formulation of effective theory which differs from the usual heavy quark effective theory (HQET) and exhibits valuable features because of the inclusion of the contributions from the antiquark fields. Matrix elements of vector and axial vector heavy quark currents between pseudoscalar and vector mesons containing a heavy quark (b or c) are then evaluated systematically up to the order of [Formula: see text] and parametrized by a set of universal form factors. With a consistent normalization condition between the effective heavy hadron states, the form factors at zero recoil are related to the ground state meson masses, which enables us to estimate the values of form factors at zero recoil. In particular, Luke's theorem comes out automatically in the new formulation of HQEFT without the need of imposing the equation of motion [Formula: see text]. Consequently, the differential decay rates of both B → D*lν and B→Dlν do not receive 1/mQ order corrections at zero recoil, which is not the case in the usual HQET. Thus we quote that the Cabibbo–Kobayashi–Maskawa matrix element |Vcb| can nicely be extracted from either of these two exclusive semileptonic decays at the order of [Formula: see text]. Our estimates for |Vcb| are presented.