Although quarks and gluons are among the fundamental building blocks of nature, experiments only directly detect hadrons, particles like the proton or pion. This phenomenology is explained using different descriptions for different situations. The language of quarks and glue uses, at short distances, of partons and, at larger distances, employs effective constituent quarks which have much larger masses than the partons. An alternative ansatz avoids talking about quarks and gluons and this is the dialect of string models and effective hadron fields. A central aim of work in Plymouth is to show how these pictures can emerge from the underlying gauge theory of quarks and gluons, Quantum Chromodynamics.
Much hadronic phenomenology is framed in terms of constituent quarks.
We have shown how to generate such gauge-invariant quarks and gluons in a systematic way which can be extended to an arbitrary order of perturbation theory. We have also demonstrated that, at short distances between the quarks, these variables correspond to the energetically favoured variables. This means that we have described the dominant gluonic configurations in hadrons at small separations between the quarks and that individual constituents are visible. It is widely accepted that such states would correspond to extremely high energies and that, as a consequence, quarks and gluons are confined inside hadrons. The difficulty for physicists is that at large separations we need non-perturbative calculations and these are hard.