Quenched lattice calculation of the vector channel [formula omitted] decay rate

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 ν . 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 B → D ⋆ ( w ) at finite momentum transfer ( w ⩾ 1 ) and at the physical values of the heavy quark masses. Our results can be used in order to extract the CKM matrix element V c b by the experimental decay rate without model dependent extrapolations. The value of V c b agrees with the one obtained from the B → D ℓ ν channel and makes us confident that the quenched approximation well applies to these transitions.