Bₛ→ Dₛ ν _ B s → D s ℓ ν ℓ near zero recoil in and beyond the Standard Model

We compute the normalization of the form factor entering the Bₛ→ Dₛ ν 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(q₀²)/f₊(q₀²)=0.77(2) , fT(q₀²,mb)/f₊(q₀²)=1.08(7) , for q₀²=11.5\ GeV² . The latter results are useful for searching the effects of physics beyond the Standard Model in Bₛ→ Dₛ ν 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 ν decay amplitude as well.