234 research outputs found
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
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