QCD Sum Rule Analysis of the Subleading Isgur-Wise Form Factor $χ_2(v\cdot v')$

Abstract

We present a QCD sum rule calculation of the spin-symmetry violating universal function $χ_2(v\cdot v')$, which appears at order $1/m_Q$ in the heavy quark expansion of meson form factors. This function vanishes in the standard approximation, where radiative effects are neglected. For the first time, the complete set of diagrams arising at order $α_s$ is evaluated. In particular, we find $χ_2(1) = -(3.8\pm 0.4)\%$ at zero recoil, indicating that $1/m_Q$ corrections induced by the chromo-magnetic moment operator are small.