One-loop amplitudes for W+3 jet production in hadron collisions
  We employ the recently developed method of generalized $D$-dimensional unitarity to compute one-loop virtual corrections to all scattering amplitudes relevant for the production of a $W$ boson in association with three jets in hadronic collisions, treating all quarks as massless. 
R. Keith Ellis, W. T. Giele, Zoltan Kunszt, Kirill Melnikov and Giulia   Zanderighi