On the universality of quark jet fragmentation

Universality of inclusive fragmentation density functions in lepton induced processes (ep, νp, e⁺e^?) and purely hadronic processes is discussed from the point of view of the Topological Expansion/Dual Unitarization Scheme. It is shown that planar, single jet dominated processes have universal inclusive distributions and average multiplicities. In multi-jet processes, treated in a simple approximation, 〈x〉 is inversely proportional to the number N of jets and the magnitude of the seagull effect increases as N².