High multiplicity QCD amplitudes with NJet.
Valery Yundin (Niels Bohr Institute, Copenhagen)

I will discuss methods relevant for accurate calculations of high-multiplicity one-loop amplitudes and their implementation in the publicly available program NJet.
NJet is a C++ library for the numerical evaluation of one-loop virtual corrections in QCD. A generalized unitarity reduction algorithm is used to construct arbitrary multiplicity fermion-gluon primitive amplitudes. From these basic building blocks the one-loop contribution to the squared matrix element, summed over colour and helicities, is calculated. While the primitive amplitudes are given for arbitrary multiplicities we provide the squared matrix elements only for up to 7 external partons allowing the evaluation of the five jet cross section at next-to-leading order accuracy.