We evaluate the important two-loop matrix element <s gamma| Q_2 | b> of the operator (cbar gamma^mu P_L b) (sbar gamma_mu P_L b) contributing to the inclusive radiative decay B -> X_s gamma. The calculation is performed in the NDR scheme, by means of asymptotic expansions method. The result is given as a series in z = m_c^2/m_b^2 up to O(z^6). We confirm the result of Greub, Hurth and Wyler obtained by a different method up to 0(z^3). Higher-order terms are found to be numerically insignificant.
Cite
@article{arxiv.hep-ph/0105160,
title = {Two-Loop Matrix Element of the Current-Current Operator in the Decay B -> X_s gamma},
author = {Andrzej J. Buras and Andrzej Czarnecki and Mikolaj Misiak and Joerg Urban},
journal= {arXiv preprint arXiv:hep-ph/0105160},
year = {2008}
}