B-Meson Wavefunction in the Wandzura-Wilczek Approximation
  The B-meson wavefunction has been studied with the help of the vacuum-to-meson matrix element of the nonlocal operators in the heavy quark effective theory. In order to obtain the Wandzura-Wilczek-type B-meson wavefunction, we solve the equations which are derived from the equation of motion of the light spectator quark in the B meson by using two different assumptions. Under the condition that $\omega_0=2\bar{\Lambda}$, the solutions for the B-meson wavefunction in this paper agree well with the one obtained by directly taking the heavy quark limit $m_b\to\infty$. Our results show that the equation of motion of the light spectator quark in the B meson can impose a strong constraint on the B-meson wavefunctions $\Psi_\pm(\omega,z^2)$. Based on the obtained results, we claim that both its distribution amplitudes $\phi_B(\omega)$ and $\bar\phi_B(\omega)$ are important for calculating the B meson decays. 
Tao Huang, Xing-Gang Wu and Ming-Zhen Zhou