Probing the Weak Boson Sector in $γe\rightarrow Ze$

Abstract

We study possible deviations from the standard model in the reaction $γe\rightarrow Ze$ at a 500 GeV $e^+e^-$ collider. As a photon source we use a laser backscattered photon beam. We investigate the most general $γZγ$ and $γZZ$ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving, $h^γ_1$ and $h^Z_1$, and two are CP-violating, $h^γ_2$ and $h^Z_2$. We present analytical expressions of the helicity amplitudes for the process $γe\rightarrow Ze$ for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the ($h^γ_1,h^Z_1$) plane at the 90\% confidence level. We then show how the angular correlation of the $Z$ decay products can be used to extract detailed information on the anomalous (especially CP-violating) $γZγ$ and $γZZ$ couplings.