Low and high energy limits of particle spectra in QCD jets

Abstract

Charged particle energy spectra in e + e − annihilation are compared with the analytical predictions from the QCD evolution equation in the Modified Leading Log Approximation. With the nonperturbative initial condition shifted down to threshold as suggested by the Local Parton Hadron Duality picture a good description of the data from the lowest up to highest available energies results. The two essential parameters in this approach are determined from a moment analysis. The sensitivity of the fit to the running of α s and to the number of active flavours (including a light gluino) is demonstrated. For very high energies the theory predicts a scaling behaviour in certain rescaled variables ("ζ-scaling"). The data show an approximate behaviour of this type in the present energy range and come close to the predicted asymptotic scaling function for the small particle energies.

Low x particle spectra in the modified leading logarithm approximation

“…(10). We use the moments calculated in [6], which are presented in the form N, ξ, σ 2 , s and k, from which we extract the first 5 K moments, and their errors are obtained by differentiating and adding in quadrature. The results are shown in Table I and Table I and in all other tables in this paper is obtained by inverting the correlation matrix, which is identified with the matrix of second derivatives.…”

Perturbative QCD description of multiparticle correlations in quark and gluon jets

“…This approach has been applied to a large variety of experimental data and found to be rather successful (see [3] for a recent review). In particular, by considering predictions which fully take into account the effects of the energy conservation law, a quantitative description of available experimental data for single particle observables, like for instance the momentum spectrum [4] and both the jet and the particle multiplicity [5], has been achieved. However, in the case of observables related to genuine multiparticle correlations, like factorial cumulants and factorial moments of the multiplicity distributions, the available theoretical predictions [6], which include only partially the energy conservation effects, do not quantitatively reproduce the experimental data [7].…”

Measurement of multiplicity and momentum spectra in the current and target regions of the Breit frame in Deep Inelastic Scattering at HERA

“…We conclude that the MLLA predictions, assuming LPHD, do not describe the data. We note however that a moments analysis has been performed [50], taking into account the limitations of the massless assumptions of the MLLA predictions, and yields good agreement between the limiting case of the MLLA [15] and e + e − data over a large energy range, 3.0 < √ s ee < 133.0 GeV. A discussion of phase space effects on the ln(1/x p ) distributions is given in ref.…”