Precision lattice QCD computation of the $B^*B\pi$ coupling

Understand

The static $B^{*}B\pi$ coupling, $\hat{g}_\chi$, a low energy constant in the leading order heavy meson chiral Lagrangian, is determined using $N_\mathrm{f} = 2$ lattice QCD.

• We use CLS ensembles with lattice spacings and pion masses down to $a = 0.05\mathrm{fm}$ and $m_{\pi}=270\mathrm{MeV}$, 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 $B^{*}$ channels ($\hat{g}_{22}$).
• Accounting for all uncertainties, which are dominated by the chiral extrapolation, we obtain $\hat{g}_\chi = 0.492(29)$, while $\hat{g}_{22}$ is somewhat smaller.