B s→D s/B→D semileptonic form-factor ratios and their application to BR(Bs0→μ +μ -)

Abstract

We calculate form-factor ratios between the semileptonic decays B ̄0→D +-ν̄ and B̄s0→Ds+ -ν̄ with lattice QCD. These ratios are a key theoretical input in a new strategy to determine the fragmentation fractions of neutral B decays, which are needed for measurements of BR(Bs0→μ +μ -). We use the MILC ensembles of gauge configurations with 2+1 flavors of sea-quarks at two s of approximately 0.12 fm and 0.09 fm. We use the model-independent z parametrization to extrapolate our simulation results at small recoil toward maximum recoil. Our results for the form-factor ratios are f0(s)(Mπ2)/f0(d)(MK2)=1.046(44) stat(15) syst and f0(s)(Mπ2)/f0(d)(Mπ2)=1.054(47) stat(17) syst. In contrast to a QCD sum-rule calculation, no significant departure from U-spin (d↔s) symmetry is observed. © 2012 American Physical Society.