Search for trilinear neutral gauge boson couplings in Z$\gamma$ production at $\sqrt{s}=189$ GeV at LEP

Abstract.

The data recorded at a centre-of-mass energy of 189 \GeV by the OPAL detector at LEP are used to search for trilinear couplings of the neutral gauge bosons in the process ${\rm e}^+{\rm e}^-\rightarrow{\rm Z\gamma}$. The cross-sections for multihadronic events with an energetic isolated photon, and for events with a high energy photon accompanied by missing energy are measured. These cross-sections and the photon energy, polar angle and isolation angle distributions are compared to the Standard Model predictions and to the theoretical expectations of a model allowing for ${\rm Z\gamma Z}$ and ${\rm Z\gamma\gamma}$ vertices. Since no significant deviations with respect to the Standard Model expectations are found, constraints are derived on the strength of neutral trilinear gauge couplings.