The Determination of $|\text{Vcb}|$ and QCD Sum Rules in Hqet

Abstract

I review recent developments in Heavy Quark Effective Theory (HQET) that lead to an almost model--independent determination of the $|\text{Vcb}|$ element of the Cabibbo--Kobayashi--Maskawa matrix from exclusive semileptonic $B\text{ra}{D}^{(\ast )}$ decays. In particular, I compare the theoretical uncertainties in the $B\text{ra}{D}^{\ast }\ell \bar{\nu }$ and the $B\text{ra}D\ell \bar{\nu }$ decay modes. I discuss the applications of QCD sum rules within HQET to semileptonic heavy meson decays and give predictions for the form factors measurable in $B\text{ra}{D}^{(\ast )}\ell \bar{\nu }$ decays.

Comments: 18pages, PHYZZX format (uses tables & epsf, figures included), WIS-93/103/Oct-PH, Invited talk at the Advanced Study Conference on Heavy Flavours, September 1993, Pavia, Italy