A planar four-loop form factor and cusp anomalous dimension in QCD
  We compute the fermionic contribution to the photon-quark form factor to four-loop order in QCD in the planar limit in analytic form. From the divergent part of the latter the cusp and collinear anomalous dimensions are extracted. Results are also presented for the finite contribution. We briefly describe our method to compute all planar master integrals at four-loop order. 
Johannes M. Henn, Alexander V. Smirnov, Vladimir A. Smirnov, Matthias   Steinhauser
hep-ph hep-th