The first lap in QCD

There is a great race on to prove that quantum chromodynamics is Nature's choice for the theory of quark interactions, and that desirable phenomena (such as quark confinement) are consequences of it. The author starts with the following basics: (1) Why we believe that quarks have colour. (2) Electric charge (QED) and colour (QCD); the fundamental interaction vertices are derived by analogy and then from the Lagrangian. (3) Renormalisation: why we do it and how it provides a mass scale in a theory which (at first sight) does not possess explicit dimensional parameters. (4a) This mass scale is arbitrary in magnitude, and physical observables cannot depend on our choice for it. This independence is expressed mathematically by the renormalisation group equation. This is solved and it is shown how an effective coupling emerges which is momentum dependent (α(Q2)). (4b) The α(Q2) is functionally related to a dimensional parameter Λ which is sometimes referred to as the scale of the strong interactions. (5) The renormalisation group equation is shown to make quantitative predictions for the Q2 dependence of the moments of structure functions in deep inelastic scattering. It is seen that these predictions do appear to be manifested in the data. (6) Some second order effects in QCD are discussed and the author reexamines what Λ means. (Auth.)