QCD TESTS AT ee Colliders

Hadronic final states of e+e− annihilations have proven to provide precise tests of the strong interaction and of its underlying theory, Quantum Chromodynamics (QCD). The success and increasing significance of QCD tests which was achieved in the past few years, especially with the precise data from LEP, was based on improvements and a deeper understanding of the theoretical predictions as well as of the experimental techniques, which both substantially profited from the experience of earlier studies with data from lower energy colliders. In fact, in many respects it seems desirable to return to the low energy e+e− data and reanalyse them with the knowledge of today. One reason behind this demand is that the size as well as the energy dependence of the strong coupling parameter αs is largest at lower energies, and thus the characteristic feature of QCD, asymptotic freedom and the running of αs, can be most significantly tested if reliable data at ‘low’ energies are available; see [1] for a recent review. In the light of these remarks, a short historical review of QCD tests in e+e− annihilation will be given in this report. In Section 2, selected highlights of early QCD studies, at energies below the Z pole, will be reviewed, and some of the original illustrations will be reproduced. Section 3 contains a brief overview of QCD tests achieved at LEP and at the SLC. In section 4, the latest measurements of αs from LEP at energies above the Z pole will be summarised. A comparison with measurements of αs from other processes will be given in Section 5, including an update of the world summary of αs determinations [1]. 2. QCD IN e+e− ANNIHILATION – FROM SPEAR TO SLC AND LEP