Role of the quark-triangle loop in D→K^*; B→D^*

Abstract

The form factors A₁, A₂ and V for D→K^* eV̅ as defined by the E 691 Collaboration are calculated via a quark-triangle loop inserted between the initial (P) and final (V) mesons, to stimulate the internal dynamics of the transition. The two hadron-quark vertex functions Γ(q), Γ'(q) are taken from the Bethe-Salpeter model pre-calibrated to hadron spectra and f_P values. The results (A₁=0.350, A₂=0.034, V=0.76) show good overlap with the E 691 measurements which claim sharp disagreement with other models. In this, the vital role of the quark triangle, and a rich interplay of mass kinematics, is emphasized. Corresponding values are predicted for B→D^*.