Quenched lattice calculation of the vector channel B --> D* l nu decay rate

TL;DR

This paper presents a quenched lattice QCD calculation of the B to D* semileptonic decay form factor, enabling a model-independent extraction of the CKM matrix element Vcb from experimental data.

Contribution

It introduces the use of the step scaling method and flavor twisted boundary conditions to accurately compute the decay form factor at physical heavy quark masses.

Findings

Vcb value agrees with B to D l nu results

Quenched approximation is reliable for these transitions

Form factor F(w) obtained at physical kinematics

Abstract

We calculate, in the continuum limit of quenched lattice QCD, the form factor that enters the decay rate of the semileptonic decay B --> D* l nu. By using the step scaling method (SSM), previously introduced to handle two scale problems in lattice QCD, and by adopting flavor twisted boundary conditions we extract F(w) at finite momentum transfer and at the physical values of the heavy quark masses. Our results can be used in order to extract the CKM matrix element Vcb by the experimental decay rate without model dependent extrapolations. The value of Vcb agrees with the one obtained from the B --> D l nu channel and makes us confident that the quenched approximation well applies to these transitions.