What happens at the end of the QCD cascades?

Abstract

This is a progress report on recent work done in Lund to describe the final steps in the QCD coherent bremsstrahlung cascades, with particular emphasis on the occurrence of a size parameter c = 11 6 in phase space. Two gluons, being interacting vector particles, will due to helicity conservation effectively stay apart a distance c, counted in generalised rapidity (a notion which I will define in the text but essentially corresponds to rapidity measured along the color flux lines of the field between the gluons). The same size c also occurs in the β-function as a measure of the region, inside which a virtual gluon splitting via reabsorbtion in the next step of perturbation theory will correspond to a “loss-term” in the Callan-Symanzik equations. Our conclusion is that at the end of the cascades when the dipole masses ( M d ) are such that log( M d 2 Λ 2 ) ⋍ nc with n a few units, then an ordered field of a helix character will emerge, i.e. a set of final “screwy gluons” are emitted in an ordered way in rapidity and azimuthal angle around the dipole axes so that the color lines are turning around.