Single jet structure ine + e − annihilation

By using JETSET 7.2 ase ⁺ e ^? event generator at different c.m. energies, we studiedsingle jet multiplicity distributions in different rapidity andp _T intervals. Good NB behavior is found and related clan structure analysis is performed. Observed differences in the behavior of the 2-and 3-jet samples can be understood in terms of the relative contribution of single quark and gluon jet to the 3-jet sample, which are obtained by selecting event by event in this sample the highest and the lowest energy jet respectively.     

Absorption and percolation in the production of J/\psi in heavy ion collisions

We present a simple model with string absorption and percolation to describe the suppression in heavy ion collisions. The model qualitatively agrees with the NA50 data, and makes precise predictions for RHIC and LHC. Received: 10 March 2000 / Published online: 6 July 2000     

Clan structure analysis and rapidity gap probability

Clan structure analysis in rapidity intervals is generalized from negative binomial multiplicity distribution to the wide class of compound Poisson distributions. The link of generalized clan structure analysis with correlation functions is also established. These theoretical results are then applied to minimum bias events and evidentiate new interesting features, which can be inspiring and useful in order to discuss data on rapidity gap probability atTevatron andHera.     

The average number of partons per clan in rapidity intervals in parton showers

The dependence of the average number of partons per clan on virtuality and rapidity variables is analytically predicted in the framework of the Generalized Simplified Parton Shower model, based on the idea that clans are genuine elementary subprocesses. The obtained results are found to be qualitatively consistent with experimental trends. This study extends previous results on the behavior of the average number of clans in virtuality and rapidity and shows how important physical quantities can be calculated analytically in a model based on essentials of QCD allowing local violations of the energy-momentum conservation law, still requiring its global validity.     

Universality of the transverse momentum distributions in the framework of percolation of strings

In the framework of percolation of color sources, the transverse momentum distribution in heavy ion and p + p collisions at all centralities and energies are shown to follow a universal behavior. The width of the distribution depends on the fluctuations of the number of color sources per cluster. At low densities, there are only independent single color sources, no fluctuations occur and the distribution is described by a single exponential. At very high densities, only one cluster of many color sources appears and therefore there are not fluctuations either and the hardness of the distribution is suppressed. The Cronin effect in this framework is due to a maximum of the fluctuations which decreases as the density increases. We obtain a good agreement with experimental data including the low p _T behavior and the spectra for different particles. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. This point is satisfied by the experimental data on p + p collisions at different energies.Received: 15 July 2004, Revised: 17 December 2004, Published online: 15 February 2005     

Hierarchical structure of correlation functions for single jets

Theoretical basis of void scaling function properties of hierarchical structure in rapidity andp _T intervals are explored. Their phenomenological consequences are analyzed at single jet level by using Monte Carlo methods ine ⁺ e ^– annihilation. It is found that void scaling function study provides an interesting alternative approach for characterizing single jets of different origin.Work supported in part by M.U.R.S.T. (Italy) under Grant 1992     

Signals of new physics in global event properties in pp collisions in the TeV energy domain: rapidity intervals

The study of possible new physics signals in global event properties in pp collisions in the TeV energy domain is extended from full phase-space to rapidity intervals experimentally accessible at LHC. The elbow structure in the total multiplicity distribution predicted in full phase-space is clearly present also in restricted rapidity intervals, leading to very strong charged particle correlations. It is also found that energy densities comparable to those reached in heavy ion collisions at RHIC could be attained in pp collisions at LHC.Received: 3 March 2004, Published online: 23 July 2004     

Clan properties in parton showers

We discuss the relationship of the forward matrix element of the operator $\bar \psi \psi $ , related to the so-called sigma term, to the quark number. We show that in the naive quark model in the canonical formalism these quantities coincide in the limit of small average quarkmomenta. In the QCD parton model defined through light-front quantization this result is preserved at leading perturbative order but it receives radiative corrections. We analyze the theoretical and phenomenological consequences of this result, which provides a bridge between a current algebra quantity, the sigma term, and a deepinelastic quantity, the parton number.     

Virtuality evolution and rapidity structure of a simplified parton shower

We have studied transverse momentum distributions for exclusive ⁰ muoproduction on protons and heavier nuclei at 2Q ²<25>². TheQ ² dependence of the slopes of thep _t ² andt distributions is discussed. The influence of the non-exclusive background is investigated. Thep _t ² -slope for exclusive events is 4.3±0.6±0.7 GeV^–2 at largeQ ². Thep _t ² spectra are much softer than inclusivep _t ² spectra of leading hadrons produced in deep inelastic scattering.Supported by Bundesministerium für Forschung und Technologie     

Large <Emphasis Type="Italic">P</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> distributions at RHIC and percolation of strings

We discuss, in the framework of percolation of strings, the general features of the transverse momentum distributions obtained at RHIC.Arrival of the final proofs: 1 April 2005PACS: 25.75.-q,12.38.Mh,24.85. + p