Evidence for a spin-1 gluon in three-jet events

High-energy e+e- qq˜g annihilation events obtained in the TASSO detector at PETRA have been used to determine the spin of the gluon in the reaction e+e− → . We analysed angular correlations between the three jet axes. While vector gluons are consistent with the data (55% confidence limit), scalar gluons are disfavoured by 3.8 standard deviations, corresponding to a confidence level of about 10−4. Our conclusion is free of possible biases due to uncertainties in the fragmentation process or in determining the qq˜g kinematics from the observed hadrons.