Extraction of Bs→Ds(*) form factors from Nf=2 lattice QCD

Abstract

We report on a two-flavor lattice QCD study of the ${B}_{s}\ensuremath{\rightarrow}{D}_{s}$ and ${B}_{s}\ensuremath{\rightarrow}{D}_{s}^{*}$ transitions parametrized, in the heavy quark limit, by the form factors $\mathcal{G}$, and ${h}_{{A}_{1}}$, ${h}_{{A}_{2}}$, and ${h}_{{A}_{3}}$, respectively. In the search for New Physics through tests of lepton flavor universality, ${B}_{s}$ 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 ${B}_{c}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}$ decays. The purpose of this exploratory two-flavor study is, in preparation for future analyses of lattice QCD simulations with ${N}_{f}>2$ and physical quark masses, to gain experience on a suitable method for a lattice extraction of form factors associated with $b\ensuremath{\rightarrow}c$ currents that may yield tighter control over systematic effects like contamination from excited states and cutoff effects. We obtain the zero-recoil values ${\mathcal{G}}^{{B}_{s}\ensuremath{\rightarrow}{D}_{s}}(1)=1.03(14)$ and ${h}^{{B}_{s}\ensuremath{\rightarrow}{D}_{s}^{*}}(1)=0.85(16)$.