|
Résumé |
Ongoing efforts to reduce the perturbative uncertainty in the B->Xs gamma decay rate have resulted in a
theory prediction to NNLO accuracy. However, a few contributions from multi-parton final states which
are formally NLO are still unknown. These are parametrically small and included in the estimated error
from higher order corrections, but must be computed if one is to claim a complete knowledge of the B-
>Xs gamma rate to NLO. A major part of these unknown pieces are four-body contributions
corresponding to the partonic process $b\to s\bar q q\gamma$. We compute these NLO four-body
contributions and confirm the corresponding tree-level LO results. While the NLO contributions arise from
tree-level and one-loop Feynman diagrams, the four-body phase-space integrations make the
computation non-trivial. The decay rate contains collinear logarithms arising from the mass regularization
of collinear divergences. We perform an exhaustive numerical analysis, and find that these contributions
are positive and amount to no more than 1% of the total rate in the SM, thus confirming previous
estimates of the perturbative uncertainty. |
