Lattice QCD calculation of (B)over-bar -> Dl(nu)over-bar decay form factors at zero recoil - art. no. 014502

A lattice QCD calculation of the (B) over bar --> Dl (v) over bar decay for m factors is presented. We obtain the value of the form factor h(+)(w) at t he zero-recoil limit w=1 with high precision by considering a ratio of corr elation functions in which the bulk of the uncertainties cancels. The other form factor h(-)(w) is calculated, for small recoil momenta, from a simila r ratio. In both cases, the heavy quark mass dependence is observed through direct calculations with several combinations of initial and final heavy q uark masses. Our results are h(+)(1) =1.007(6)(2)(3) and h(-)(1)=-0.107(28) (04)(10/30). For both the first error is statistical; the second sterns fro m the uncertainty in adjusting the heavy quark masses and the last from omi tted radiative corrections. Combining these results, we obtain a precise de termination of the physical combination FB --> D(1) =1.058(20/17), where th e mentioned systematic errors are added in quadrature. The dependence on la ttice spacing and the effect of quenching are not yet included, but with ou r method they should be a fraction of FB --> D-1.