Review of QCD at LEP

We review the first round of QCD studies at the c+ ecollider LEP, which started operating towards the end of last year. These studies at the peak of the 2’ resonance have proven to be extremely rewarding, not only because of the large statistics available due to the high resonance cross section, but also because of the higher centre of mass energy, which allows a much cleaner study of events with multiple jets. For example, 20% of the events show a clean S-jet structure in which the least energetic jet has an average energy of 20 GeV. Such events originate from quark-antiquark-gluon (gqg) states, in which the least energetic jet is usually the gluon jet. Therefore, at LEP energies the gluon jets are considerably ‘healthier’ than at the PEP and PETRA colliders, where the energies were typically three times lower. The higher jet energy gives a better collimation of the jets and therefore a better jet axis determination and separation between the jets. This improves many QCD studies, especially the study of gluon jets and the angular correlations in I-jet events, from which one can hope to isolate the triple gluon vertex contribution. This gluon self interaction is the hallmark of the non-abelian character of QCD and is thought to be responsible for the confinement of quarks inside the nuclei. The topics to be discussed here are: