Measurement of three-jet distributions sensitive to the gluon spin ine+e− annihilations at GeV

Three-jet variables constructed from multi-hadronic events produced byZ0 decays are compared to theoretical calculations assuming a vector gluon or a hypothetical scalar gluon. The data yield conclusive direct evidence for the former case. The distributions of the reduced energy of the second-most energetic jet and of the cosine of the Ellis-Karliner angle are chosen to demonstrate this effect.