The B → D∗ℓv Form factor at zero recoil

We describe a model independent lattice QCD method for determining the deviation from unity for hA1 (1), the B → D∗lv form factor at zero recoil. We extend the double ratio method previously used to determine the B → Dlv form factor. The bulk of statistical and systematic errors cancel in the double ratios we consider, yielding form factors which promise to reduce present theoretical uncertainties in the determination of |Vcb|. We present results from a prototype calculation at a single lattice spacing corresponding to β = 5.7.