Precision lattice QCD computation of the B⁎BπB⁎Bπ coupling

The static B⁎BπB⁎Bπ coupling, gˆχ, a low energy constant in the leading order heavy meson chiral Lagrangian, is determined using Nf=2Nf=2 lattice QCD. We use CLS ensembles with lattice spacings and pion masses down to a=0.05 fma=0.05 fm and mπ=270 MeVmπ=270 MeV, and perform combined continuum and chiral extrapolations of our results which have a much better accuracy than previous numbers in the literature. As a by-product, we determine the coupling between the first radial excitations in the B   and B⁎B⁎ channels (gˆ22). Accounting for all uncertainties, which are dominated by the chiral extrapolation, we obtain gˆχ=0.492(29), while gˆ22 is somewhat smaller. The comparison to a precise quenched computation suggests that there is little influence by the sea quarks and gˆχ will not change much when a dynamical strange quark is included.