Reduction of the planar double-box diagram for single-top production via auxiliary mass flow

The single-top production is an important process at the LHC to test the Standard Model and search for the new physics beyond the Standard Model. Although the complete next-to-next-to-leading order QCD correction to the single-top production is crucial, this calculation is still challenging at present. In order to efficiently reduce the next-to-next-to-leading order single-top amplitude, we improve the auxiliary mass flow method by introducing the $\epsilon$ truncation. For demonstration we choose one typical planar double-box diagram for the $tW$ production. It is shown that one coefficient of the form factors on its amplitude can be systematically reduced into the linear combination of 198 scalar integrals.

Figure 1

Double-box diagram for the $tW$ production.