A Comparison of the Momentum Spectra in Deep Inelastic Scattering with the Modified Leading Logarithmic Approximation

The evolution of the logarithmic scaled energy spectra with energy scale, in the framework of the modified leading logarithmic approximation (MLLA), is investigated. The behaviour of the higher order moments of HERA deep inelastic scattering data are compared with the analytic predictions of MLLA.Comment: 9 pages incl 4 figure

Perturbative universality in QCD jet physics

I survey some recent advances in the applications of the analytical perturbative approach to the description of particle distributions in multi-jet processes. New tests of the perturbatively based picture in the (semi) soft region are discussed.Comment: LaTeX, 15 pages, talk at the XXVII International Symposium on Multiparticle Dynamics, Frascati (Rome), Italy, 8-12 September 199

Hadronic Antenna Patterns as a Probe of Leptoquark Production at HERA

Hadronic antenna patterns can provide a valuable diagnostic tool for probing the origin of the apparent excess of high $x,Q^2$ events at HERA. We present quantitative predictions for the distributions of soft particles and jets in standard deep inelastic scattering $eq \to eq$ events and in events corresponding to the production of a narrow colour-triplet scalar (`leptoquark') resonance. The corresponding distributions of soft photon radiation, which are sensitive to the leptoquark electric charge, are also presented. The distribution for one particular leptoquark assignment is shown to contain a radiation zero.Comment: 16 pages, LaTeX, incl. 6 postscript figures, uses epsfig.sty. (High resolution pictures may be obtained via email.

Inclusive hadronic distributions in jets and sub-jets with jet axis from color current

The hadronic \kt-spectrum and the gluon to quark average multiplicity ratio $r=N_g/N_q$ inside a high energy sub-jet are determined from a precise definition of the jet axis, including corrections of relative magnitude ${\cal O}(\sqrt{\alpha_s})$ with respect to the Modified Leading Logarithmic Approximation (MLLA), in the limiting spectrum approximation (assuming an infrared cut-off Q_0 =\lqcd). The results for the \kt-spectrum in the limiting spectrum approximation are found to be, after normalization, in impressive agreement with measurements by the CDF collaboration and the ratio has not been measured yet.Comment: Invited lecture at Ringberg Workshop: New Trends in HERA Physics 2008, October 5-10, 2008, Ringberg Castle, Tegernsee-Bavaria, German

Jet Fractions in e+e- Annihilation

The jet fractions expected in e+e- annihilation are calculated analytically in the leading log approximation up to 6 jet order for both the JADE and Durham algorithms.Comment: 19 pages, 2 figure

Fragmentation in DIS

The fragmentation properties in deep-inelastic scattering (DIS) at HERA are investigated in order to test perturbative QCD and quark fragmentation universality. Selected results for the inclusive single particle distributions and the angular two-particle correlations in the current region of the Breit frame are presented and compared to results from $e^{+}e^{-}$ collisions. The extension of the DIS fragmentation studies to the target region of the Breit frame are also reported.Comment: 3 pages, 4 figures, Proc. of the 7th Int. Workshop on Deep Inelastic Scattering and QCD (DIS99), Zeuthen, Germany, April 19-23, 1999, to appear in Nucl. Phys. B (Proc. Suppl.

Perturbative QCD Description of Mean Jet and Particle Multiplicities in e+e- annihilation

A complete numerical solution of the evolution equation for parton multiplicities in quark and gluon jets with initial conditions at threshold is presented. Data on both hadron and jet multiplicities in e+e- annihilation are well described with a common normalization, giving further support to the picture of Local Parton Hadron Duality. Predictions for LEP-II energies are presented. Furthermore we study the sensitivity to the cutoff parameter Q_0 and the scale of alpha_s.Comment: LaTeX, 7 pages, 3 figures, uses espcrc2.sty, to appear in Proc. of XXVII International Symposium on Multiparticle Dynamics, Frascati, Italy, September 1997, Nucl Phys. B (Proc. Suppl.

Progress and Problems in QCD - Report from the Hadronic Final States Working Group at DIS99

We present a summary of the Hadronic Final States parallel sessions of the DIS99 Workshop. Topics were presented over two days and included both theoretical and experimental talks. Recent progress in the understanding of QCD in deep inelastic scattering, e^+e^- collisions, and in gamma and p collisions was discussed.Comment: 15 pages, 22 figures, Latex, nbp.sty. To be published in the Proceedings of DIS'99, Zeuthen, Germany, 19-23 April 199

Local charge compensation from colour preconfinement as a key to the dynamics of hadronization

If, as is commonly accepted, the colour-singlet, `preconfined', perturbative clusters are the primary units of hadronization, then the electric charge is necessarily compensated locally at the scale of the typical cluster mass. As a result, the minijet electric charge is suppressed at scales that are greater than the cluster mass. We hence argue, and demonstrate by means of Monte Carlo simulations using HERWIG, that the scale at which charge compensation is violated is close to the mass of the clusters involved in hadronization, and its measurement would provide a clue to resolving the nature of the dynamics. We repeat the calculation using PYTHIA and find that the numbers produced by the two generators are similar. The cluster mass distribution is sensitive to soft emission that is considered unresolved in the parton shower phase. We discuss how the description of the splitting of large clusters in terms of unresolved emission modifies the algorithm of HERWIG, and relate the findings to the yet unknown underlying nonperturbative mechanism. In particular, we propose a form of $\alpha_S$ that follows from a power-enhanced beta function, and discuss how this $\alpha_S$ that governs unresolved emission may be related to power corrections. Our findings are in agreement with experimental data.Comment: 37 pages, 20 figure

Low x particle spectra in the Modified Leading Logarithm Approximation

We show that the higher moments of the evolution obtained from the Modified Leading Logarithm Approximation may be regarded as spurious higher order terms in perturbation theory, and that neglecting them leads to a good description of the data around and above the peak in $\xi=\ln (1/x)$. Furthermore, we use this study of the moments to show that at high energy the Limiting Spectrum with Local Parton-Hadron Duality may also be derived from the Modified Leading Logarithm Approximation without any non-perturbative assumptions.Comment: Submitted to Eur. Phys. J.,