Amplitude Zeros in $W^{\pm }Z$ Production

Abstract

We demonstrate that the Standard Model amplitude for $f_1{\bar{f}}_2\to W^{\pm }Z$ at the Born-level exhibits an approximate zero located at $\cos \theta =(g_{-}^{f_1}+g_{-}^{f_2})/(g_{-}^{f_1}-g_{-}^{f_2})$ at high energies, where the $g_{-}^{f_i}$ ($i=1,2$) are the left-handed couplings of the $Z$-boson to fermions and $\theta$ is the center of mass scattering angle of the $W$-boson. The approximate zero is the combined result of an exact zero in the dominant helicity amplitudes $\mathcal{M}(\pm ,\mp )$ and strong gauge cancelations in the remaining amplitudes. For non-standard $WWZ$ couplings these cancelations no longer occur and the approximate amplitude zero is eliminated.

Comments: 11 pages, 4 figures submitted separately as uuencoded tar-ed postscript files, FSU-HEP-940307, UCD-94-5