Hadron multiplicity as the limit of jet multiplicity at high resolution

Abstract

Recently exact numerical results from the evolution equation for parton multiplicities in QCD jets have been obtained. A comparison with various approximate results is presented. A good description is obtained not only of the jet multiplicities measured at LEP-1 but also of the hadron multiplicities for $cms$ energies above 1.6 GeV in \epem annihilation. The solution suggests that a final state hadron can be represented by a jet in the limit of small (nonperturbative) $k_{\perp }$ cut-off $Q_0$. In this description using as adjustable parameters only the QCD scale $\Lambda$ and the cut-off $Q_0$, the coupling ${\alpha }_s$ can be seen to rise towards large values above unity at low energies.

Comments: LaTex, 4 pages, 2 figures, presented at HEP Int. Euroconf. on Quantum Chromodynamics, Montpellier, July 1997