ABSTRACT
This chapter introduces Quantum Chromodynamics (QCD) and discusses some of its simpler experimental consequences. It recalls the evidence for the ‘colour’ degree of freedom and then describes the dynamics of colour, and the QCD Lagrangian. Perhaps the most remarkable thing about the dynamics of QCD is that, despite its being a theory of the strong interactions, there are certain kinematic regimes – roughly speaking, short distances or high energies – in which it is effectively a quite weakly interacting theory. In appropriate cases, the lowest-order perturbation theory amplitudes (tree graphs) provide a very convincing qualitative, or even ‘semi-quantitative’, orientation to the data. The chapter shows how the tree graph techniques acquired for QED in volume 1 produce more useful physics when applied to QCD. It introduces the dimensionless jet mass variables.
