Exclusive semileptonic decays of B mesons into light mesons in the relativistic quark model

Abstract

The exclusive semileptonic $B\to \pi (\rho )e\nu$ 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 $\pi (\rho )$ meson allows for the expansion of the decay form factors at $q^2=0$ in the inverse powers of $b$-quark mass. This considerably simplifies the analysis of these decays. The $1/m_b$ expansion is carried out up to the first order. It is found that the $q^2$-dependence of the axial form factor $A_1$ is different from the $q^2$-behaviour of other form factors. We find $\Gamma (B\to \pi e\nu )=(3.1\pm 0.6)\times |V_{ub}{|}^2\times 10^{12}$s${}^{-1}$ and $\Gamma (B\to \rho e\nu )=(5.7\pm 1.2)\times |V_{ub}{|}^2\times 10^{12}$s${}^{-1}$. The relation between semileptonic and rare radiative $B$-decays is discussed.

Comments: 11 pages, Latex, 3 figures