A measurement of the QCD colour factor ratiosCA/CF andTF/CF from angular correlations in four-jet events

From 1 105 045 hadronic Z0 decays observed with the OPAL detector at the LEP e+e− collider, 21 732 four-jet events are selected. A simultaneous fit of three selected angular variables from these events by the second order QCD matrix element calculation yieldsCA/CF=2.11±0.16(stat.)±0.28(syst.)TF/CF=0.40±0.11(stat.)±0.14(syst.) for the ratios of colour factors, in agreement with SU(3) expectations ofCA/CF=9/4 andTF/CF=3/8.