Statistical J/psi production and open charm enhancement in Pb+Pb collisions at CERN SPS

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. Charmed quarks and antiquarks are assumed to be created at the initial stage of the reaction and their number is conserved during the evolution of the system. They are distributed among open and hidden charm hadrons at the hadronization stage in accordance with laws of statistical mechanics. The model is in excellent agreement with the experimental data on J/psi production in lead-lead collisions at CERN SPS and predicts strong enhancement of the open charm multiplicity over the standard extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A possible mechanism of the charm enhancement is proposed.Comment: Presented at 6th International Conference on Strange Quarks in Matter, Frankfurt am Main, 2001. 4 pages, LaTeX, 1 PS-figur

The Breathing Modes of the B=2B=2 Skyrmion and the Spin-Orbit Interaction

The coupling of the breathing and rotational modes of the skyrmion-skyrmion system leads to a nucleon-nucleon spin-orbit interaction of short range, as well as to spin-orbit potentials for the transitions $NN \to N(1440)N$, $NN \to NN(1440)$ and $NN \to N(1440)N(1440)$. The longest range behaviour of these spin-orbit potentials is calculated in closed form.Comment: Latex, figures not include

A model-independent analysis of the dependence of the anomalous J/psi suppression on the number of participant nucleons

A recently published experimental dependence of the J/psi to Drell-Yan ratio on the measured, by a zero degree calorimeter, forward energy E_ZDC in Pb+Pb collisions at the CERN SPS is analyzed. Using a model-independent approach it is shown that the data are at variance with an earlier published experimental dependence of the same quantity on the transverse energy of neutral hadrons E_T. The discrepancy is related to a moderate centrality region: 100 < N_p < 200 (N_p is the number of participant nucleons) and is peculiar only to the data obtained within the `minimum bias' analysis (using the `theoretical Drell-Yan'). This could result from systematic experimental errors in the minimum bias sample. A possible source of the errors is discussed.Comment: 10 pages, LaTeX, 3 PS-figures. V2: Misprints are correcte

J/psi Suppression and Enhancement in Au+Au Collisions at the BNL RHIC

We consider the production of the J/psi mesons in heavy ion collisions at RHIC energies in the statistical coalescence model with an exact (canonical ensemble) charm conservation. The c\bar{c} quark pairs are assumed to be created in the primary hard parton collisions, but the formation of the open and hidden charm particles takes place at the hadronization stage and follows the prescription of statistical mechanics. The dependence of the J/psi production on both the number of nucleon participants and the collision energy is studied. The model predicts the J/psi suppression for low energies, whereas at the highest RHIC energy the model reveals the J/psi enhancement.Comment: 14 pages, REVTeX, 3 PS-figure

Statistical Coalescence Model Analysis of J/psi Production in Pb+Pb Collisions at 158 A GeV

Production of J/\psi mesons in heavy ion collisions is considered within the statistical coalescence model. The model is in agreement with the experimental data of the NA50 Collaboration for Pb+Pb collisions at 158 A GeV in a wide centrality range, including the so called ``anomalous'' suppression domain. The model description of the J/psi data requires, however, strong enhancement of the open charm production in central Pb+Pb collisions. This model prediction may be checked in the future SPS runs.Comment: 13 pages, REVTeX, 2 PS-figure