Form factors for B → πlνl and B → K∗γ decays on the lattice Original Research Article

We present a unified method for analysing form factors in B → πlνl and B → K∗γ decays. The analysis provides consistency checks on the q2 and 1M extrapolations necessary to obtain the physical decay rates. For the first time the q2 dependence of the form factors is obtained at the B scale. In the B → πlνl case, we show that pole fits to f+ may not be consistent with the q2 behaviour of f0, leading to a possible factor of two uncertainty in the decay rate and hence in the value of |Vub|2 deduced from it. For B → K∗γ, from the combined analysis of form factors T1 and T2, we find the hadronisation ratio RK∗ of the exclusive B → K∗γ to the inclusive b → sγ rates is of order 35% or 15% for constant and pole-type behaviour of T2, respectively.