J. Tran Thanh Van

Dual parton model

Soft multiparticle production is a dominant feature of most events in high energy hadronic collisions. Since soft processes have no large momentum transfer, perturbative QCD expansions in the strong coupling constant are not applicable. However, suitable large N expansions of QCD provide a topological classification of diagrams and a potentially useful non-perturbative approach. This topological expansion, when supplemented with generally accepted theoretical principles like duality, unitarity, Regge behavior and the parton structure of hadrons, provides the basis underlying the dual parton model (DPM). This model has been extensively studied and gradually extended over the past twelve years. It has been shown that DPM provides a complete, phenomenological description of all facets of soft processes. This is a non-trivial achievement in view of the large amount of soft multiparticle data available from both hadronic as well as nuclear beams and targets. Here, we describe the basic ideas of the model and review the main results coming from DPM.

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.

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.

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.

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.

Particle densities in SS and PbPb collisions at RHIC and LHC energies in the dual parton model

Abstract The density of charged particles in nucleus-nucleus collisions is computed in the framework of the dual parton model including the effect of multiple inelastic scattering in the individual nucleon-nucleon collisions. Numerical calculations for SS and PbPb collisions at mid rapidities are presented.

Minijets and the real part of the elastic amplitudes

Abstract In the framework of the perturbative reggeon calculus, including a hard pomeron, we perform a fit of pp and p p total, elastic and diffractive cross section data and the ratio ϱ. The parameters of the hard pomeron are deduced from the minijet cross section measured by the UA1 Collaboration. We obtain a value of the real part of the p p elastic amplitude compatible with the recent UA4 measurement.

Evidence for “held-back” valence quarks from particle ratios in pp and pp collisions

Abstract We show that recently measured particle ratios in the central region of pp and p p collisions give valuable information on the fate of valence quarks in a soft hadronic collision, indicating that a valence quark from each initial hadron is “held back” with a small momentum fraction. This mechanism is a key feature of the dual parton fragmentation approach to low- p T multiparticle production.

J/ψ suppression in nuclear collisions revisited

Abstract We study a particular type of final state interaction which gives a decrease of the parameter α, characterizing the mass number dependence, with increasing values of x F . Using this final state interaction for a produced J/ψ we compute, in the framework of the dual parton model, the E T -distributions of events with either J/ψ or Drell-Yan pair production in O-U collisions-which are in qualitative agreement with available data in the large E T region.