Hyperon Enhancement in the Dual Parton Model

We review the two sources of hyperon enhancement in the dual parton model: strings originating from diquark-antidiquark pairs in the nucleon sea and net baryons containing two or three sea quarks with a yield controlled by the observed stopping. We show that adding final state interactions (including strangeness exchange reactions as well as the inverse reactions required by detailed balance) with a single averaged cross-section $\sigma=0.2$ mb, we can explain the observed hyperon enhancement in PbPb collisions at CERN SPS.Comment: 6 pages, 2 eps-figure

Mechanisms of multiparticle production in heavy ion collisions at high energy

In the framework of a microscopic string model inclusive charged particle distribution and baryon and antibaryon production are described. The emphasis is put on high energies (RHIC) where shadowing corrections play a crucial role. Some recent developments on $J/\psi$ suppression at CERN-SPS are also discussed. Possible consequences for the crucial issue of thermal equilibration of the produced system are considered.Comment: 35 pages, Latex style, 12 Figures, 2 Tables. To be published in a special issue of ``Acta Physica Polonica'' in homage to Jan Kwiecinsk

Centrality Dependence of Hadron Multiplicities in Nuclear Collisions in the Dual Parton Model

We show that, even in purely soft processes, the hadronic multiplicity in nucleus-nucleus interactions contains a term that scales with the number of binary collisions. In the absence of shadowing corrections, this term dominates at mid rapidities and high energies. Shadowing corrections are calculated as a function of impact parameter and the centrality dependence of mid-rapidity multiplicities is determined. The multiplicity per participant increases with centrality with a rate that increases between SPS and RHIC energies, in agreement with experiment.Comment: 15 pages, 4 postscript figure

Coherence Effects in Charmonium Production off Nuclei : Consequences for J/\psi Suppression

The probabilistic Glauber formula for nuclear absorption used in the literature is only valid at low energies and $x_+ \simeq 0$. Due to energy conservation, $\sigma_{abs}$ is replaced by an effective cross-section $\sigma_{abs} + x_+^{\gamma}$ ($\sigma_{c\bar{c}-N} - \sigma_{abs})$ which increases with $x_+$ and tends to the total $c\bar{c}-N$ cross-section $\sigma_{c\bar{c}-N}$. Experimental data can be described with $\sigma_{abs} \sim 4 \div 5$mb and $\sigma_{c\bar{c}-N} \sim 15 \div 20$mb. At high energies, due to the increase of the coherence length, this formula changes. The main change is the replacement of $\sigma_{abs}$ by $\sigma_{c\bar{c}-N}$ -- for all values of $x_+$, as $s \to \infty$. Thus, if $\sigma_{c\bar{c}-N} > \sigma_{abs}$ the $J/\psi$ suppression due to nuclear interaction will increase with energy.Comment: Talk presented at the International Workshop on Charm Production, ECT*, Trento, June 200

The Primakoff effect on a proton target

Primakoff effect offers us with a way to determine the radiative decay width of pseudo-scalar mesons when they are photo-produced in the electromagnetic field of hadronic systems. Taking advantage of recent developments in the Regge description of the production of mesons in the strong hadronic field, this paper evaluates the relative importance of the electromagnetic and the strong amplitudes, and assesses the possibilities which become opened by modern experimental facilities.Comment: 4 pages; 5 Figure

Elliptic Flow in a Final State Interaction Model

We propose a final state interaction model to describe the fixed $p_T$ suppression of the yield of particles at all values of $p_T$. We make an extension of the model to the motion in the transverse plane which introduces a dependence of the suppression on the azimuthal angle $\theta_R$. We obtain values of the elliptic flow $v_{2}$ close to the experimental ones for all values of $p_T$.Comment: 4 pages, 6 figures, proceedings of XLIst Rencontres de Moriond: QCD and Hadronic Interactions at high energ

Multiplicities and J/ψJ/\psi suppression at LHC energies

We present our predictions on multiplicities and $J/\psi$ suppression at LHC energies. Our results take into account shadowing effects in the initial state and final state interactions with the hot medium. We obtain 1800 charged particles at LHC and the $J/\psi$ suppression increases by a factor 5 to 6 compared to RHIC.Comment: 2 pages, 2 figures. Contributed to Workshop on Heavy Ion Collisions at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun 200

Large transverse momentum suppression at RHIC: Shadowing and absorption

We propose a model of suppression of $\pi^0$'s based on two different effects: at low $p_T$ we take into account the shadowing corrections, which are non-linear and essential for the description of the inclusive spectra, while at large $p_T$ the suppression is produced through the interaction of the large $p_T$ pion with the dense medium created in the collision. The main features of the data on $AuAu$ and $dAu$ collisions at RHIC energies are reproduced both at mid and at forward rapidities.Comment: 6 pages, 2 figures. Contribution to the 8th Workshop on Non-Perturbative Quantum Chromodynamics, June 7-11, 2004, l'Institut Astrophysique de Paris, Franc

Baryon and Antibaryon production at RHIC energies in the Dual Parton Model

We compute the mid-rapidity densities of pions, kaons, baryons and antibaryons in $Au$--$Au$ collisions at $\sqrt{s}$ = 130 GeV in the Dual Parton Model supplemented with final state interactions, and we present a comparison with available data.Comment: 4 pages, 2 figures. Talk given at XXXVII Rencontres de Moriond, Les Arcs, France, March 200