Heavy-meson form factors from QCD sum rules.

Abstract

A consistent framework is developed for studying hadronic form factors of heavy mesons using QCD sum rules in the heavy-quark effective theory, including the next-to-leading-order renormalization-group improvement. Sum rules are derived for the asymptotic value of the meson decay constant {ital f}{sub {ital P}} and for the universal Isgur-Wise form factor. It is shown that renormalization-group effects considerably enhance the prediction for {ital f}{sub {ital P}} and bring its asymptotic value in accordance with recent lattice results. Including finite-mass corrections, the dependence of the physical decay constant on the meson mass is investigated. We obtain {ital f}{sub {ital D}}{congruent}170{plus minus}30 MeV and {ital f}{sub {ital B}}{congruent}190{plus minus}50 MeV. The origin of the breakdown of the heavy-quark expansion for {ital f}{sub {ital D}} is analyzed. In the case of heavy-meson transition form factors, both the QCD and 1/{ital m}{sub {ital Q}} corrections are moderate and under control. A sum rule for the renormalized Isgur-Wise function is derived and evaluated. The theoretical result is compared to experimental data.