A. Capella

Jets in small-pT hadronic collisions, universality of quark fragmentation, and rising rapidity plateaus

Abstract We consider a two-rapidity-chain fragmentation model for small- p T hadronic collisions based on the dual topological approach. This model, when supplemented by the universality of quark fragmentation functions, accounts for the energy and x -dependence of all available one particle inclusive data. The model provides a novel explanation for the rise of hadronic plateaus with energy.

Structure functions and low x physics

Abstract In the framework of conventional Regge theory we present a common description of total photon-proton cross-section and proton structure functions in the region 0≤Q2≤5 GeV2. Using it as an initial condition in the perturbative QCD evolution equation, we describe structure functions at any Q2 and x-including the small x region explored at HERA.

A new parton model description of soft hadron-nucleus collisions

Abstract We present a parton model description of small p T hadron nucleus collisions based on a two-chains parton model for hadron-hadron collisions. The model provides a quantitative description of single particle spectra — including the leading particle effect — in terms of standard quark fragmentation and momentum distribution functions.

Multiplicity distributions up to √s = 540 GeV in the dual parton model

Abstract We compute the average charge multiplicities and dispersions in proton-proton and antiproton-proton interactions up to SPS collider energies in the framework of a multi-chain dual parton model. The corresponding data for deep inelastic lepton-proton and e + e − reactions are used as the sole input. The height of the central plateau is also computed.

Jψ and ψ′ suppression in heavy ion collisions

Abstract We study the combined effect of nuclear absorption and final state interaction with co-moving hadrons on the J ψ and ψ′ suppression in proton-nucleus and nucleus-nucleus collisions. We obtain a reasonable description of the PbPb data using theoretically meaningful values of the cross-sections involved and without introducing any discontinuity in the J ψ or ψ′ survival probabilities. However, the description of both pA and SU data is significantly worse than the one obtained with nuclear absorption alone.

Diffractive dissociation in deep inelastic scattering at HERA

Abstract The diffraction dissociation of virtual photons is considered in the framework of conventional Regge theory. It is shown that the recent HERA data on large rapidity gap events can be successfully described in terms of the pomeron structure function. Using Regge factorization, the latter can be related to the deuteron structure function. The parameters which relate these two structure functions are determined from soft hadronic diffraction data. The size of the shadowing corrections at low x and large Q 2 is also obtained.

High-energy nucleus-nucleus inelastic interactions in the dual parton model

Abstract Rapidity distributions of particles produced in a high-energy nucleus-nucleus interaction, are computed in the framework of the dual-parton model. Finite energy effects reduce the asymptotic value of the multiplicity densities given by the multiple scattering Glauber-Gribov scheme. This reduction is unambiguously determined from the particle production mechanism specific to the dual-parton model. Simple expressions are obtained, which are successfully compared with preliminary data on α-α collisions at ISR.

Behaviour of the proton-proton total cross section at ISR energies in the reggeon calculus

Abstract We study the behaviour of σ pp T at ISR energies in the Reggeon calculus with a bare triple Pomeron coupling non vanishing at q 2 = 0. The parameters are determined from elastic and inclusive data. A sizable increase of σ T with s can only be obtained when the bare Pomeron intercept is such that the renormalized Pomeron singularity is above one, in the forward direction.

Novel mechanism of nucleon stopping in heavy ion collisions

Abstract When a diquark does not fragment directly but breaks in such a way that only one of its quarks gets into the produced baryon, the latter is produced closer to mid rapidities. The relative size of this diquark breaking component increases quite fast with increasing energy. We show that a given energy it also increases with the atomic mass number and with the centrality of the collision and that it allows to explain the rapidity distribution of the net baryon number ( p- p ) in SS central collisions. Predictions for PbPb collisions are presented.

Strangeness production in the Dual Parton model

Abstract Production of strange mesons and baryons is studied in a Monte Carlo Dual Parton model for hadron-hadron, hadron-nucleus and nucleus-nucleus collisions with standard strangeness suppression in the chain fragmentation and enhanced strangeness (up to a SU(3) symmetric sea) at the sea chain ends. Additionally, (qq)-( q q ) production from the sea has been introduced into the chain formation process with the same probability as for the q → qq branching within the chain fragmentation. Rapidity distributions and multiplicity ratios are in reasonable agreement with recent experimental data.