Speaker: Hannes JEREMIE
Title

Abstract
We report on two measurements using multijet final states from hadronic decays of the Z^0 obtained with the OPAL detector at LEP. In the first analysis we extracted the QCD colour factors C_A and C_F together with alpha_s(M_z) from the comparison of the data to the next-to-leading order predictions of four-jet angular correlations and matched next-to-leading order and next-to-leading logarithmic approximations for multi-jet rates. In the second analysis the four-jet angular correlations alone are used to investigate various aspects of four-jet physics related to the colour factor ratio T_R/C_F, obtained by comparing the data to second (=leading) order matrix models. In particular the distribution of this quantity as a function of the invariant mass of the two least energetic jets is qualitatively reproduced by hybrid second order matrix element models coupled with a parton shower mechanism.