Numerical solutions to Giovannini’s QCD parton branching processes

In 1979, Giovannini [1] formulated multiparticle production as a manifestation of four QCD processes: A: g → gg (gluon bremsstrahlung), A-: q → qg (quark bremsstrahlung), B: g → qq (quark pair creation) and C: g → ggg (four-gluon vertex). At present, only approximate solutions exist, such as the Generalized Multiplicity Distribution (GMD) which excludes pro- cesses B and C [2, 3]. These approximate solutions have been very successful in describing charged particle multiplicities at lower energies, at least until the appearance of a shoulder-like structure at √s ≈ 200 GeV and 900 GeV first reported by the UA5 collaboration [4], also known as “KNO-scaling violation”. Here, we extend the work of Sakai [5] and attempt a numerical solution that incorporates all four QCD processes, and see if the addition of processes B and C can explain the shoulder-like structure.

The discovery of the gluon

Soon after the postulation of quarks, it was suggested that they interact via gluons, but direct experimental evidence was lacking for over a decade. In 1976, Mary Gaillard, Graham Ross and the author suggested searching for the gluon via 3-jet events due to gluon bremsstrahlung in e+ e- collisions. Following our suggestion, the gluon was discovered at DESY in 1979 by TASSO and the other experiments at the PETRA collider.