Effective Field Theory Approach to Parton-Hadron Conversion in High Energy QCD Processes

A QCD based effective action is constructed to describe the dynamics of confinement and symmetry breaking in the process of parton-hadron conversion. The deconfined quark and gluon degrees of freedom of the perturbative QCD vacuum are coupled to color singlet collective fields representing the non-perturbative vacuum with broken scale and chiral symmetry. The effective action recovers QCD with its scale and chiral symmetry properties at short space-time distances, but yields at large distances (r > 1 fm) to the formation of symmetry breaking gluon and quark condensates. The approach is applied to the evolution of a fragmenting $q\bar q$ pair with its generated gluon distribution, starting from a large hard scale $Q^2$. The modification of the gluon distribution arising from the coupling to the non-perturbative collective field results eventually in a complete condensation of gluons. Color flux tube configurations of the gluons in between the $q\bar q$ pair are obtained as solutions of the equations of motion. With reasonable parameter choice, the associated energy per unit length (string tension) comes out $\simeq 1$ GeV/fm, consistent with common estimates.

K. Geiger · 1994