Formation of charmonium states in heavy ion collisions and thermalization of charm

We examine the possibility to utilize in-medium charmonium formation in heavy ion interactions at collider energy as a probe of the properties of the medium. This is possible because the formation process involves recombination of charm quarks which imprints a signal on the resulting normalized transverse momentum distribution containing information about the momentum distribution of the quarks. We have contrasted the transverse momentum spectra of J/Psi, characterized by , which result from the formation process in which the charm quark distributions are taken at opposite limits with regard to thermalization in the medium. The first uses charm quark distributions unchanged from their initial production in a pQCD process, appropriate if their interaction with the medium is negligible. The second uses charm quark distributions which are in complete thermal equilibrium with the transversely expanding medium, appropriate if a very strong interaction between charm quarks and medium exists. We find that the resulting of the formed J/Psi should allow one to differentiate between these extremes, and that this differentiation is not sensitive to variations in the detailed dynamics of in-medium formation. We include a comparison of predictions of this model with preliminary PHENIX measurements, which indicates compatibility with a substantial fraction of in-medium formation.Comment: 8 pages, 5 figures, based on presentation at the Workshop on Quark-Gluon-Plasma Thermalization (QGPTH05), Vienna, Austria, August 10-12, 2005. To be published in the proceedings. Two figures and 3 references update

An assessment of J/Psi formation in the light of initial RHIC data

Predictions of J/Psi formation at RHIC via "off-diagonal" combinations of charm and anticharm quarks in a region of color deconfinement are confronted with initial data from the PHENIX collaboration. We find that the measured centrality behavior places significant constraints on the various parameters which control model calculations of J/Psi formation. Within present statistical and systematic uncertainties, one can map out a region of parameter space within which the contribution of formation in a deconfined phase is allowed. As these uncertainties decrease and new data from d-Au interactions becomes available, it is expected that definitive tests for the presence of this formation mechanism will be possible. We anticipate that the rapidity and transverse momentum spectra will prove decisive for a final determination.Comment: 6 pages, 5 figures, presented at SQM2003, March 12-17, 2003. To be published in J. Phys.

Nonlinear Behavior of Quarkonium Formation and Deconfinement Signals

We anticipate new features of quarkonium production in heavy ion collisions at RHIC and LHC energies which differ from a straightforward extrapolation of results at CERN SPS energy. General arguments indicate that one may expect quarkonium formation rates to increase more rapidly with energy and centrality than the production rate of the heavy quarks which they contain. This is due to new formation mechanisms in which independently-produced quarks and antiquarks form a bound quarkonium state. This mechanism will depend quadratically on the total number of initially-produced heavy quark pairs, and becomes numerically significant only at RHIC and LHC energy. When viewed as a signal of color deconfinement, a transition from suppression to enhancement may be observed. Explicit model calculations are presented, in which one can follow striking variations of final quarkonium production within a range of parameter space.Comment: To appear in the proceedings of Pan American Advanced Studies Institute on New States of Matter in Hadronic Interactions (PASI 2002), Campos do Jordao, Brazil, 7-18 Jan 2002; American Institute of Physics 200

In-Medium formation of J/Psi as a probe of charm quark thermalization

Charmonium formation via charm quark in-medium recombination in heavy ion interactions at collider energies has the potential to probe some properties of the medium by utilizing the sensitivity of the recombination process to the momentum distribution of the quarks. We have examined the transverse momentum spectra of J/Psi, characterized by , which result from the formation process in which the charm quark distributions are unchanged from their initial production in a pQCD process. This is contrasted with the case in which the charm quarks have completely come into thermal equilibrium with an expanding medium whose properties are determined by the spectra of produced light hadrons. We find that the resulting of the formed J/Psi provide a distinct signature of the underlying charm quark spectra, and that signature is essentially independent of the detailed dynamics of the in-medium formation reaction. In addition, both of these signatures are sufficiently separated from the case in which no in-medium formation takes place. Finally, utilizing a model for the fraction of J/Psi which originate from in-medium formation, we predict the centrality behavior of these signatures.Comment: 6 pages, 4 figures, invited talk at the 35'th International Symposium on Multiparticle Dynamics 2005, Kromeriz, Czech Republic, to be published in the proceeding

Quarkonium formation in statistical and kinetic models

I review the present status of two related models addressing scenarios in which the formation of heavy quarkonium states in high energy heavy ion collisions proceed via "off-diagonal" combinations of a quark and an antiquark. The physical process involved belongs to a general class of quark "recombination", although technically the recombining quarks here were never previously bound in a quarkonium state. Features of these processes relevant as a signature of color deconfinement are discussed.Comment: 6 pages, 8 figures, based on invited plenary talk at Hard Probes 2004, Ericeira, Portugal, November 3-11, 2004, to appear in the proceeding

Momentum spectra of charmonium produced in a quark-gluon plasma

We calculate rapidity and transverse momentum distributions of charmonium formed in high energy heavy ion collsions from incoherent recombination of charm quarks. The results are very sensitive to the corresponding distributions of the charm quarks, and thus can serve as a probe of the state of matter produced in the heavy ion collision. At one extreme we generate a set of charm pair momenta directly from pQCD amplitudes, which are appropriate if one can neglect interaction of the quarks with the medium. At the other extreme we generate momenta of charm quarks in thermal equilibrium with the expanding medium, appropriate for an extremely strong interaction. Explicit predictions are made for J/Psi formation in Au-Au interactions at RHIC. We find that for the case in which charm quark momenta are unchanged from the pQCD production calculation, both the rapidity and transverse momentum spectra of the formed J/Psi are substantially narrower than would be anticipated in scenarios which do not include the in-medium formation. In particular, the average transverse momentum of the J/Psi will exhibit a non-monotonic behavior in the progression from p-p to p-A to A-A interactions.Comment: Final published version, clarifying remarks adde

Suppression of Quarkonium Production in Heavy Ion Collisions at RHIC and LHC

A model for the production of quarkonium states in the midrapidity region at RHIC and LHC energy range is presented which explores well understood properties of QCD only. An increase of the quarkonium hadronisation time with the initial energy leads to a gradual change of the most important phenomena from fixed target- to collider-energies. We evaluate nuclear effects in the quarkonium production due to medium modification of the momentum distribution of the heavy quarks produced in the hard interactions, i.e. due to the broadening of the transverse momentum distribution. Other nuclear effects, i.e. nuclear shadowing and parton energy loss, are also evaluated.Comment: 5 pages, 1 table, 1 figure, Contribution to the Proceedings of the V International Conference on Strangeness in Quark Matter July 20-25, 2000 Berkeley, Californi