Tree-level contributions to B -> Xs gamma
Abstract
Weak radiative decay B -> X_s gamma is known to be a loop-generated process. However, it does receive tree-level contributions from CKM-suppressed b -> u ubar s gamma transitions. In the present paper, we evaluate such contributions together with similar ones from the QCD penguin operators. For a low value of the photon energy cutoff E_0 ~ m_b/20 that has often been used in the literature, they can enhance the inclusive branching ratio by more than 10%. For E_0 = 1.6 GeV or higher, the effect does not exceed 0.4%, which is due to phase-space suppression. Our perturbative results contain collinear logarithms that depend on the light quark masses m_q (q=u,d,s). We have allowed m_b/m_q to vary from 10 to 50, which corresponds to values of m_q that are typical for the constituent quark masses. Such a rough method of estimation may be improved in the future with the help of fragmentation functions once the considered effects begin to matter in the overall error budget for BR(B -> X_s gamma).
Cite
@article{arxiv.1209.0965,
title = {Tree-level contributions to B -> Xs gamma},
author = {Maciej Kaminski and Mikolaj Misiak and Michal Poradzinski},
journal= {arXiv preprint arXiv:1209.0965},
year = {2014}
}
Comments
v3: Corrected factors of 2 in the subdominant T_3 contributions. Minor changes in the numerical results (Table II)