Study of QCD Coherence in Hadronic Z decays

We present studies of QCD Coherence phenomenom, well know as the Angluar Ordering (AO), which has been predicted by QCD theory. The analysis is based on the Particle-Particle-Correlation-Asymetery (PPCA) and on the Energy-Mutiplicity-Mutiplicity-Correlation (EMMC) functions, as observables sensitive to Angular Ordering. The Monte Carlo programs and a sample of 800000 hadronic events registered by ALEPH detector in 1992 and 1993 were used in this analysis. We find that the data favors Monte Carlo programs with AO, which supports the QCD prediction.