Semi-leptonic four-fermion final states in polarised γγ reactions: Exact results vs. an improved narrow width approximation

We calculate the process γγ → e− ν̄ud̄ with the full set of Feynman diagrams. We consider different implementations of the W width and different combinations of the photon polarisations. The results of an improved narrow width approximation based on γγ → W+W− with full spin-correlations that takes into account different angular cuts as well as cuts on the invariant masses are compared to those of the complete calculation.