Relativistic description of the exclusive rare radiative decays ofBmesons

The exclusive rare radiative $B$-decays are studied in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The large recoil momentum of the final vector meson allows for the expansion of the decay form factor in inverse powers of the b-quark mass. This considerably simplifies the analysis of these decays. The $1/m_b$ expansion is carried out up to the second order. The form factor of \btok decay is found to be $F_1^{B\to K^* \gamma}(0)=0.32\pm 0.03 $ and it leads to $BR(B\to K^*\gamma )= (4.5\pm 1.5) \times 10^{-5}$, which is in agreement with the recent CLEO data. The form factors of the decays \btorho, \bstophi and \bstok are also considered. The relation between rare radiative and semileptonic $B$-decays into light vector meson is discussed.