20 research outputs found
Thermal versus Direct Production in Ultrarelativistic Heavy-Ion Collisions
The production of mesons in central collisions of heavy nuclei is
investigated as a function of collision energy. Two contributions are
considered simultaneously: early (hard) production coupled with subsequent
suppression in a Quark-Gluon Plasma, as well as thermal recombination of
primordially produced and quarks at the hadronization transition.
Whereas the former still constitutes the major fraction of the observed
abundance at SpS energies, the latter dominates the yield at RHIC. The
resulting excitation function for the number of 's over open charm
pairs exhibits nontrivial structure around AGeV, evolving
into a significant rise towards maximal RHIC energy. We study this feature
within different (thermal) scenarios for suppression, including
parton-induced quasifree destruction as a novel mechanism.Comment: 6 pages ReVTeX, including 4 eps-figures; Revised version accepted for
publication in Phys. Lett.
Theoretical Overview on (Hidden) Charm in High-Energy Heavy-Ion Collisions
Recent developments in the theoretical evaluation of charmonium production in
ultrarelativistic heavy-ion collisions (URHIC's) are discussed. In particular,
the consequences of equilibrium properties of open and hidden charm states --
accessible, {\it e.g.}, in QCD lattice gauge calculations -- are assessed.
These include abundances as well as formation and dissociation rates of
charmonia in both hadronic and quark-gluon matter.Comment: Invited Talk at 7. Int. Conf. on Strangeness in Quark Matter
(Atlantic Beach, NC, USA, 12.-17.03.03); 10 pages LaTeX including 11 Figures
and iop style files; v3: Section 3.4 (Continuity) revise
Two-Component Approach to Production in High-Energy Heavy-Ion Collisions
The production of charmonia in ultrarelativistic heavy-ion collisions is
investigated including two sources. These are a primordial contribution coupled
with various phases of dissociation, and a statistical coalescence of and
quarks at the hadronization phase transition. Within a schematic
fireball evolution, SPS data on production can be reasonably well
reproduced. Remaining discrepancies in the ratio are discussed.
Predictions for the centrality dependence at RHIC energies are
confronted with first data from PHENIX. The pertinent excitation function of
the ratio exhibits a characteristic minimum structure
signaling the transition from the standard suppression scenario (SPS)
to predominantly statistical production (RHIC).Comment: 4 pages (incl. 4 postscript figures); v2: Typos corrected; uses
espcrc1.sty. Talk given at Quark Matter 2002, Nantes, July 18-24, 2002, to
appear in the proceedings in Nucl. Phys.
Medium Modifications of Charm and Charmonium in High-Energy Heavy-Ion Collisions
The production of charmonia in heavy-ion collisions is investigated within a
kinetic theory framework simultaneously accounting for dissociation and
regeneration processes in both quark-gluon plasma (QGP) and hadron-gas phases
of the reaction. In-medium modifications of open-charm states (c-quarks,
D-mesons) and the survival of J/psi mesons in the QGP are included as inferred
from lattice QCD. Pertinent consequences on equilibrium charmonium abundances
are evaluated and found to be especially relevant to explain the measured
centrality dependence of the psi'/psi ratio at SPS. Predictions for recent
In-In experiments, as well as comparisons to current Au-Au data from RHIC, are
provided.Comment: 4 Latex pages including 4 eps figures and IOP style files. Talk given
at the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus
Collisions, Quark Matter 2004, Oakland, CA USA, 11-17 Jan 2004. To appear in
J. Phys.
Bottomonium Production at RHIC and LHC
Properties of bottomonia (Upsilon, chi_b and Upsilon') in the Quark-Gluon
Plasma (QGP) are investigated by assessing inelastic reaction rates and their
interplay with open-bottom states (b-quarks or B-mesons) and color-screening.
The latter leads to vanishing quarkonium binding energies at sufficiently high
temperatures (close to the dissolution point), which, in particular, renders
standard gluo-dissociation, g+Upsilon -> b + b-bar, inefficient due to a
substantial reduction in final-state phase space. This problem is overcome by
invoking a "quasifree" destruction mechanism, g,q,q-bar + Upsilon -> g,q,q-bar
+ b + b-bar, as previously introduced for charmonia. The pertinent reaction
rates are implemented into a kinetic theory framework to evaluate the time
evolution of bottomonia in heavy-ion reactions at RHIC and LHC within an
expanding fireball model. While bottom quarks are assumed to be exclusively
produced in primordial nucleon-nucleon collisions, their thermal relaxation
times in the QGP, which importantly figure into Upsilon-formation rates, are
estimated according to a recent Fokker-Planck treatment. Predictions for the
centrality dependence of Upsilon production are given for upcoming experiments
at RHIC and LHC. At both energies, Upsilon suppression turns out to be the
prevalent effect.Comment: 16 Pages, 21 figures, 1 table v2: Manuscript reorganized, several
sections moved to appendices, additional comments included, contents
unchange
Dileptons in High-Energy Heavy-Ion Collisions
The current status of our understanding of dilepton production in
ultrarelativistic heavy-ion collisions is discussed with special emphasis on
signals from the (approach towards) chirally restored and deconfined phases. In
particular, recent results of the CERN-SPS low-energy runs are compared to
model predictions and interpreted. Prospects for RHIC experiments are given.Comment: Invited talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; 1 Latex and
9 eps-/ps-files Reoprt No.: SUNY-NTG-02-0
Charmonium Suppression and Regeneration from SPS to RHIC
The production of charmonia is investigated for heavy-ion collisions from SPS
to RHIC energies. Our approach incorporates two sources of yield: (i)
a direct contribution arising from early (hard) parton-parton collisions,
subject to subsequent nuclear absorption, quark-gluon plasma and hadronic
dissociation, and (ii) statistical production at the hadronization transition
by coalescence of and quarks. Within an expanding thermal
fireball framework, the model reproduces centrality dependencies
observed at the SPS in Pb-Pb and S-U collisions reasonably well. The study of
the ratio at SPS points at the importance of the hadronic phase
for interactions, possibly related to effects of chiral symmetry
restoration. Predictions are given for the centrality dependence of the
ratio at full RHIC energy. We also calculate the
excitation function of this ratio. The latter exhibits a characteristic minimum
structure signalling the transition from the standard suppression
scenario prevailing at SPS to dominantly thermal regeneration at collider
energies.Comment: 17 pages, 15 figure
Lattice calculations of meson correlators and spectral functions at finite temperature
I review recent progress in relating meson spectral function to imaginary
time correlation function at finite temperature calculated on isotropic as well
as on anisotropic lattices. Special attention is payed for the lattice
artifacts present in calculation of meson spectral functions. Results in the
case of light quarks as well as heavy quarks are reviewed which indicate in
particular that even in the chiral limit meson spectral functions have
non-trivial structure and the ground state quarkonia survive up to temperature
1.5T_cComment: Invited plenary talk presented at SQM03 (Atlantic Beach, March 12-17,
2003), 10 pages LaTeX, uses iopams.sty, iopart.cl
Thermal width and gluo-dissociation of quarkonium in pNRQCD
The thermal width of heavy-quarkonium bound states in a quark-gluon plasma
has been recently derived in an effective field theory approach. Two phenomena
contribute to the width: the Landau damping phenomenon and the break-up of a
colour-singlet bound state into a colour-octet heavy quark-antiquark pair by
absorption of a thermal gluon. In the paper, we investigate the relation
between the singlet-to-octet thermal break-up and the so-called
gluo-dissociation, a mechanism for quarkonium dissociation widely used in
phenomenological approaches. The gluo-dissociation thermal width is obtained by
convoluting the gluon thermal distribution with the cross section of a gluon
and a 1S quarkonium state to a colour octet quark-antiquark state in vacuum, a
cross section that at leading order, but neglecting colour-octet effects, was
computed long ago by Bhanot and Peskin. We will, first, show that the effective
field theory framework provides a natural derivation of the gluo-dissociation
factorization formula at leading order, which is, indeed, the singlet-to-octet
thermal break-up expression. Second, the singlet-to-octet thermal break-up
expression will allow us to improve the Bhanot--Peskin cross section by
including the contribution of the octet potential, which amounts to include
final-state interactions between the heavy quark and antiquark. Finally, we
will quantify the effects due to final-state interactions on the
gluo-dissociation cross section and on the quarkonium thermal width.Comment: 17 pages, 6 figure
Heavy quarkonia in a medium as a quantum dissipative system: Master-equation approach
The problem of the evolution of a heavy quarkonium in a medium can be recast
as that of a quantum dissipative system. Within the framework of the
master-equation approach to open quantum systems, we consider the real-time
dynamics of quarkonia. We find that in a plasma at fixed temperature, the
populations of the various quarkonium states evolve together, while their
momentum distribution satisfies a Fokker-Planck equation.Comment: 12 pages, 8 figures. Version 2 matches the published versio