We study the helicity amplitudes and the observables of the process $\gamma \gamma \to \gamma Z$ at high energy. As in the case of the $\gamma \gamma \to \gamma\gamma$ process studied before, the relevant diagrams in the standard model (SM) involve $W$, charged quark and lepton loops; while in SUSY we also have contributions from chargino, and charged sfermion or Higgs loop diagrams. Above 250 GeV, the dominant SM amplitudes are themselves dominated by the $W$ loop, and as for $\gamma \gamma \to \gamma \gamma$, they are helicity conserving and almost purely imaginary. We discuss the complementary information provided by $\gamma \gamma \to \gamma Z$ for the identification of possible non standard effects. This process, together with $\gamma \gamma \to \gamma \gamma$, should provide very useful information on the nature of possible new physics particles, above the threshold of their direct production.
Categories: hep-ph