Precision for B-meson matrix elements

TL;DR

This paper combines HQET and the Step Scaling Method in quenched lattice QCD to precisely determine B-meson properties, including the b-quark mass and B_s-meson decay constant, with results consistent with experimental data.

Contribution

It demonstrates an improved precision method for B-physics observables by combining HQET and Step Scaling, applicable to full QCD in future work.

Findings

F_Bs = 191(6) MeV

M_b = 6.88(10) GeV

m_b(m_b) = 4.42(6) GeV

Abstract

We demonstrate how HQET and the Step Scaling Method for B-physics, pioneered by the Tor Vergata group, can be combined to reach a further improved precision. The observables considered are the mass of the b-quark and the B_s-meson decay constant. The demonstration is carried out in quenched lattice QCD. We start from a small volume, where one can use a standard O(a)-improved relativistic action for the b-quark, and compute two step scaling functions which relate the observables to the large volume ones. In all steps we extrapolate to the continuum limit, separately in HQET and in QCD for masses below m_b. The physical point m_b is then reached by an interpolation of the continuum results in 1/m. The essential, expected and verified, feature is that the step scaling fuctions have a weak mass-dependence resulting in an easy interpolation to the physical point. With r_0=0.5fm and the experimental B_s and K masses as input, we find F_Bs=191(6)MeV and the renormalization group invariant mass M_b=6.88(10)GeV, translating into m_b(m_b)=4.42(6)GeV in the MSbar scheme. This approach seems very promising for full QCD.