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

TL;DR

This paper presents a high-precision lattice QCD calculation of the $B^*B\pi$ coupling, providing improved accuracy and insights into the effects of sea quarks on this low energy constant.

Contribution

The study offers the most precise determination to date of the static $B^*B\pi$ coupling using $N_f=2$ lattice QCD with continuum and chiral extrapolations.

Findings

$\hat{g}_\chi = 0.492(29)$ with all uncertainties accounted for.

The coupling between first radial excitations, $\hat{g}_{22}$, is smaller.

Sea quarks have little influence on $\hat{g}_\chi$.

Abstract

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. The comparison to a precise quenched computation suggests that there is little influence by the sea quarks and $\hat{g}_\chi$ will not change much when a dynamical strange quark is included.