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

Abstract

We calculate the process $\gamma \gamma \to e^{-}{\bar{\nu }}_{e}u\bar{d}$ 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 $\gamma \gamma \to W^{+}{W}^{-}$ 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.

Comments: paper in LATEX, 19 pages, 3 figures. Complete psfile available via anonymous ftp at ftp://lapphp0.in2p3.fr/pub/preprints-theorie/enslapp635.uu or at http://lapphp0.in2p3.fr/preplapp/psth/enslapp635.ps.gz