427 research outputs found
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 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 , and . 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
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 yield in the most central collisions.Comment: 5 pages, RevTeX4, 1 PS-figure. V2: The final PHENIX data are analyze
- âŠ