FORM-FACTORS FOR B-]PI-L(V)OVER-BAR(L) AND B-]K-ASTERISK-GAMMA DECAYS ON THE LATTICE

We present a unified method for analysing form factors in B --> pi l ($) over bar nu(l) and B --> K*gamma decays. The analysis provides consistency checks on the q(2) and 1/M extrapolations necessary to obtain the physical decay rates. For the first time the q(2) dependence of the form factors is obtained at the B scale. In the B --> pi l ($) over bar nu(l) case, we show that pole fits to f(+) may not be consistent with the q(2) behaviour of f(0), leading to a possible factor of two uncertainty in the decay rate and hence in the value of /V-ub/(2) deduced from it. For B --> K*gamma, from the combined analysis of form factors T-1 and T-2, we find the hadronisation ratio R(K)* of the exclusive B --> K*gamma to the inclusive b --> s gamma rates is of order 35% or 15% for constant and pole-type behaviour of T-2, respectively.