QCD coherence studies using two particle azimuthal correlations

From a sample of 146900 hadronicZ0 decays recorded by the OPAL detector at LEP, we have studied the azimuthalcorrelations of particles in hadronic events. It is expected that these correlations are sensitive to interference effects in QCD. We have compared the data to QCD Monte Carlo models which include and which do not include interference effects. We find that the distributions of azimuthalcorrelations are not reproduced by the parton showermodels we have tested unless interference effects are included, no matter which hadronisation scheme is used.