Search for trilinear neutral gauge boson couplings in Zγ production at √s = 189 GeV at LEP

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.