Perturbative QCD Correction to the $B\to\pi$ Transition Form Factor

We report on the perturbative $O(\alpha_s)$ correction to the light-cone QCD sum rule for the $B\to \pi$ transition form factor $f^+$. The correction to the product $f_Bf^+$ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding $O(\alpha_s)$ correction in the two-point sum rule for $f_B$. The resulting cancellation of large QCD corrections in $f^+$ eliminates one important uncertainty in the sum-rule prediction for this form factor.