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

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

Charm coalescence at relativistic energies

The J/psi yield at midrapidity at the top RHIC (relativistic heavy ion collider) energy is calculated within the statistical coalescence model, which assumes charmonium formation at the late stage of the reaction from the charm quarks and antiquarks created earlier in hard parton collisions. The results are compared to the new PHENIX data and to predictions of the standard models, which assume formation of charmonia exclusively at the initial stage of the reaction and their subsequent suppression. Two versions of the suppression scenario are considered. One of them assumes gradual charmonium suppression by comovers, while the other one supposes that the suppression sets in abruptly due to quark-gluon plasma formation. Surprisingly, both versions give very similar results. In contrast, the statistical coalescence model predicts a few times larger $J/\psi$ yield in the most central collisions.Comment: 5 pages, RevTeX4, 1 PS-figure. V2: The final PHENIX data are analyze

ДОСЛІДЖЕННЯ ПАРАМЕТРІВ ІМПУЛЬСУ ДЕФОРМАЦІЙНОЇ ХВИЛІ ПРИ ПОВЕРХНЕВО ПЛАСТИЧНОМУ ЗМІЦНЕННІ

The article considers the issue of increasing the efficiency of shock energy and recording equipment for the study of the parameters of the deformation wave pulse. The review of the last researches and publications is carried out and perspective directions at designing of the special measuring equipment are established. A method is proposed and an experimental-measuring complex for the study of the momentum parameters in the deformation zone under different initial conditions is developed. The study of the parameters, of the shock pulse and micro hardness, of the strengthened material in the deformation zone using different versions, of the impact systems. It is established that when using a shock system with a step-shaped striker, the shock wave is characterized by a complex shape of the pulse. To assess the reliability of the obtained results, a test problem was solved in the environment of the Abaqus software package. When designing new technological processes of strengthening, the results of experimental studies such as the impact system and the parameters and modes of the processing process are of particular importance. It is established that the best result is shown by shock systems, which allow forming a prolonged shock pulse.The article considers the issue of increasing the efficiency of shock energy and recording equipment for the study of the parameters of the deformation wave pulse. The review of the last researches and publications is carried out and perspective directions at designing of the special measuring equipment are established. A method is proposed and an experimental-measuring complex for the study of the momentum parameters in the deformation zone under different initial conditions is developed. The study of the parameters, of the shock pulse and micro hardness, of the strengthened material in the deformation zone using different versions, of the impact systems. It is established that when using a shock system with a step-shaped striker, the shock wave is characterized by a complex shape of the pulse. To assess the reliability of the obtained results, a test problem was solved in the environment of the Abaqus software package. When designing new technological processes of strengthening, the results of experimental studies such as the impact system and the parameters and modes of the processing process are of particular importance. It is established that the best result is shown by shock systems, which allow forming a prolonged shock pulse

The High E_T Drop of J/psi to Drell-Yan Ratio from the Statistical c anti-c Coalescence Model

The dependence of the J/psi yield on the transverse energy E_T in heavy ion collisions is considered within the statistical c anti-c coalescence model. The model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the high-E_T region (E_T > 100 GeV). Here E_T-fluctuations and E_T-losses in the dimuon event sample naturally create the celebrated drop in the J/psi to Drell-Yan ratio.Comment: 14 pages, REVTeX, 1 PS-figure. v2: References are corrected and update