The decay of the upsilon into photons and gluons

Abstract The hadronic decays of heavy quark-antiquark 1 3 S 1 resonances such as the ψ J or ϒ can provide an ideal laboratory for studying the properties of gluon jets. We discuss the predictions of QCD perturbation theory for gluon-jet structures, hadronic multiplicities, fragmentation distributions, and angular distributions. In particular the channel (Q Q → γ + X , whose rate, spectrum, and angular distribution are predicted in lowest order, should allow the study of the jet and resonance structure produced via two intermediate gluons.