  We compute the normalization of the form factor entering the Bs --> Ds l nu
decay amplitude by using numerical simulations of QCD on the lattice. From our
study with Nf=2 dynamical light quarks, and by employing the maximally twisted
Wilson quark action, we obtain in the continuum limit G(1) = 1.052(46). We also
compute the scalar and tensor form factors in the region near zero recoil and
find f0(t0)/f+(t0)=0.77(2), fT(t0,mb)/f+(t0)=1.08(7), for t0=11.5 GeV^2. These
latter results are useful for searching the effects of physics beyond the
Standard Model in Bs --> Ds l nu decays. Our results for the similar form
factors relevant to the non-strange case indicate that the method employed here
can be used to achieve the precision determination of the B --> D l nu decay
amplitude as well.

High Energy Physics - Lattice;High Energy Physics - Experiment;High Energy Physics - Phenomenology