Scenarios for particle production in the GeV and TeV regions are reviewed. The expected increase with the c.m. energy of the average number of clans for the soft component and the decrease for the semihard one indicate possible classical and quantum behavior of gluons, respectively. Clan thermodynamics, discussed in the paper, appears as the natural framework to deal with such phenomena.

The spectra of charged particles in the energy variable $\xi = \log 1/x$ (``the hump backed plateau'') are analyzed in terms of moments in order to investigate the sensitivity to the running of $\alpha_s$ in particular towards small scales, and to further test thereby the local parton hadron duality picture. The modified leading log approximation (MLLA) of QCD provides a very satisfying description of the $e^+e^-$ data in the full range of c.m. energies from about 1 up to 91 GeV. The same calculation but with fixed coupling $\alpha_s$ yields moments which are inconsistent with the data already close to threshold. In particular the soft particles ($E\le 1$~GeV) reflect directly the running of $\alpha_s$.Comment: 14 pages including 3 figures, uuencoded gz-compressed PS-fil

The analytical perturbative approach, if taken to the limit of its applicability, allows one to predict an energy independent limit for the one-particle invariant density in QCD jets E dn d 3 p at very small momenta p. This is a direct consequence of the colour coherence in soft gluon branching. The existing data on the charged and identified particle inclusive spectra follow this prediction surprisingly well. Further tests of the perturbatively based picture in the soft region are discussed. 1

The evolution equation for parton multiplicities in quark and gluon jets which takes into account the soft gluon interference is solved numerically using the initial conditions at threshold. If the k ⊥ -cutoff Q c is lowered towards the hadronic scale Q 0 of a few hundred MeV, the jets are fully resolved into hadrons. Both hadron and jet multiplicities in e + e − annihilation are well described with a common normalization. Evidence is presented within this perturbative approach that the coupling α s (k ⊥ ) rises by an order of magnitude when approaching the low energy region. The ratio of hadron multiplicities in gluon and quark jets is found smaller than in previous approximate solutions of the evolution equation.

The recent data from LEP-1.5 on charged particle spectra are analyzed within the analytical QCD approach.Comment: LaTeX, 14 pages with 2 Postscript figures, uses epsfig.st