The $B^*B\pi$ coupling with relativistic heavy quarks

Abstract

We report on a calculation of the B * Bπ coupling in lattice QCD. The strong matrix element Bπ|B * is directly related to the leading order low-energy constant in heavy meson chiral perturbation theory (HMχPT) for B-mesons. We carry out our calculation directly at the b-quark mass using a non-perturbatively tuned clover action that controls discretisation effects of order | pa| and (ma) n for all n. Our analysis is performed on RBC/UKQCD gauge configurations using domain wall fermions and the Iwasaki gauge action at two lattice spacings of a −1 = 1.73(3) GeV, a −1 = 2.28(3) GeV, and unitary pion masses down to 290 MeV. We achieve good statistical precision and control all systematic uncertainties, giving a final result for the HMχPT coupling g b = 0.569(48) stat (59) sys in the continuum and at the physical light-quark masses. This is the first calculation performed directly at the physical b-quark mass and lies in the region one would expect from carrying out an interpolation between previous results at the charm mass and at the static point.

The form factor for $B$ to $\pi$ semileptonic decay from 2+1 flavors of domain-wall fermions

“…where I 1 (m ll ) = m 2 ll log(m 2 ll /Λ 2 ) and f π = 130.4 MeV [15]. For the parameter g, we use g B * Bπ = 0.569 calculated as a part of this RHQ project [16]. Fig.…”