$Wγγ$ Production at the Fermilab Tevatron Collider: Gauge Invariance and Radiation Amplitude Zero

Abstract

The electroweak process $p\bar p \to \ell^\pmνγγ$ is calculated at tree level, including finite W width effects. In order to obtain a gauge invariant amplitude, the imaginary parts of $WWγ$ triangle graphs and $WWγγ$ box diagrams have to be included, in addition to resumming the imaginary contributions to the W polarization. We demonstrate the existence of a radiation amplitude zero in $p\bar p \to W^\pm γγ\to \ell^\pmνγγ$, and discuss how it may be observed in correlations of the $γγ$ and lepton rapidities at the Fermilab Tevatron.