Perturbative QCD approach and particle energy spectra

The Modified Leading Log Approximation of QCD and the local parton hadron duality picture are shown to give a fully satisfactory description of data on charged particle energy spectra in $e^+e^-$ annihilation. The analysis of data in terms of moments points out the running of $\alpha_s$ both at very low $cms$ energy (${\cal O}$(3 GeV)) and at very low particle energy (${\cal O}$(200-500 MeV)). The study of the universal soft limit of energy spectra at low particle energy is proposed as a test of QCD coherence. The extension of this approach at identified particles' spectra is discussed.