Finite Width Effects and Gauge Invariance in Radiative $W$ Production and Decay

Abstract

The naive implementation of finite width effects in processes involving unstable particles can violate gauge invariance. For the example of radiative $W$ production and decay, $q\bar q' \to \ell\nu\gamma$, at tree level, it is demonstrated how gauge invariance is restored by including the imaginary part of triangle graphs in addition to resumming the imaginary contributions to the $W$ vacuum polarization. Monte Carlo results are presented for the Fermilab Tevatron.Comment: 10 pages, Revtex, 3 figures submitted separately as uuencoded tarred postscript files, the complete paper is available at ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.Z or http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-878.ps.