Extraction of $B_s\to D_s^{(*)}$ form factors from $N_f$=2 lattice QCD

International audienceWe report on a two-flavor lattice QCD study of the Bs→Ds and Bs→D∗s transitions parametrized, in the heavy quark limit, by the form factors G, and hA1, hA2, and hA3, respectively. In the search for New Physics through tests of lepton flavor universality, Bs decay channels are complementary to the B decays widely studied at B factories and LHCb, while on the theory side they can be better controlled than the Bc and Λb decays. The purpose of this exploratory two-flavor study is, in preparation for future analyses of lattice QCD simulations with Nf>2 and physical quark masses, to gain experience on a suitable method for a lattice extraction of form factors associated with b→c currents that may yield tighter control over systematic effects like contamination from excited states and cutoff effects. We obtain the zero-recoil values GBs→Ds(1)=1.03(14) and hBs→D∗s(1)=0.85(16)