An estimate of the B-->K*gamma form factor

Abstract

We present the results of a lattice QCD calculation of the form factor relevant to B-->K*gamma decay. Our final value, T(0) = 0.24 +/- 0.03(+0.04/-0.01), is obtained in the quenched approximation, and by extrapolating T(q2=0;H--> K*)MH^(3/2) from the directly accessed H-heavy mesons to the meson B. We also show that the extrapolation from B-->K*gamma* to B-->K*gamma leads to a result consistent with the one quoted above. On the other hand, our results are not accurate enough to solve the SU(3) flavor breaking effects in the form factor and we quote T(q2=0;B--> K*)/T(q2=0;B-->rho)=1.2(1), as our best estimate.