Uncertainty in the leading-order perturbative QCD calculations of B-meson decays

Uncertainty in the perturbative quantum chromodynamics (PQCD) calculation of B decays is investigated in B→π, B→D transition form factors and B→Dπ decay amplitudes. B-meson distribution amplitude dependence is studied by taking three kinds of distribution amplitudes suggested so far. It is found that almost the same q2 dependence of the form factors can be obtained irrespective of the types of the B-meson distribution amplitudes by suitably choosing one parameter. The B→Dπ process shows the difference due to the distribution amplitude. The effect of the subleading component of the B-meson distribution amplitude is also studied in the three processes. The numerical results of calculations with the subleading component can be well approximated by the leading-order calculation with a suitable choice of the distribution amplitude parameters.