3,549 research outputs found
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.
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
Protein polymorphisms in strains of golden hamsters
At present only a few data is available about biochemical polymorphisms in the golden hamster. But the great number of strains of this species used in biomedical research requires the establishment of specific marker traits which can be used forgenetic control purposes.This study gives an overview on the degree of variability on the protein level among a series of 17 strains of hamsters.The results show 9 of about 40 stained isoproteins to express electrophoretic variants (22.5 %). Unexpectedly most of the phenotypes occur not only between but also within the strains despite more than 25 generations of inbreeding.The reason for this level of heterogeneity is not yet really obvious. Several possible points of influence are discussed, 0.3. an increased mutation rate or physiological specificities. At present, nongenetic reasons seem to be the most likely explanationfor most of the polymorphisms
Statistical Complexity and Nontrivial Collective Behavior in Electroencephalografic Signals
We calculate a measure of statistical complexity from the global dynamics of
electroencephalographic (EEG) signals from healthy subjects and epileptic
patients, and are able to stablish a criterion to characterize the collective
behavior in both groups of individuals. It is found that the collective
dynamics of EEG signals possess relative higher values of complexity for
healthy subjects in comparison to that for epileptic patients. To interpret
these results, we propose a model of a network of coupled chaotic maps where we
calculate the complexity as a function of a parameter and relate this measure
with the emergence of nontrivial collective behavior in the system. Our results
show that the presence of nontrivial collective behavior is associated to high
values of complexity; thus suggesting that similar dynamical collective process
may take place in the human brain. Our findings also suggest that epilepsy is a
degenerative illness related to the loss of complexity in the brain.Comment: 13 pages, 3 figure
Signatures of Thermal Dilepton Radiation at RHIC
The properties of thermal dilepton production from heavy-ion collisions in
the RHIC energy regime are evaluated for invariant masses ranging from 0.5 to 3
GeV. Using an expanding thermal fireball to model the evolution through both
quark-gluon and hadronic phases various features of the spectra are addressed.
In the low-mass region, due to an expected large background, the focus is on
possible medium modifications of the narrow resonance structures from
and mesons, whereas in the intermediate-mass region the old idea of
identifying QGP radiation is reiterated including effects of chemical
under-saturation in the early stages of central Au+Au collisions.Comment: 17 pages ReVTeX including 16 figure
The Vector Probe in Heavy-Ion Reactions
We review essential elements in using the channel as a probe for
hot and dense matter as produced in (ultra-) relativistic collisions of heavy
nuclei. The uniqueness of the vector channel resides in the fact that it
directly couples to photons, both real and virtual (dileptons), enabling the
study of thermal radiation and in-medium effects on both light () and heavy () vector mesons. We emphasize the importance
of interrelations between photons and dileptons, and characterize relevant
energy/mass regimes through connections to Quark-Gluon-Plasma emission and
chiral symmetry restoration. Based on critical analysis of our current
understanding of data from fixed-target energies, we identify open key
questions to be addressed.Comment: Invited Talk at the Hot Quarks 2004 Workshop, July 18-24, 2004 (Taos
Valley, NM, USA), 15 pages latex incl 14 figs and iop style files, to appear
in the proceeding
Two-photon decays of vector mesons and dilepton decays of scalar mesons in dense matter
Two-photon decays of vector mesons and dilepton decays of scalar mesons which
are forbidden in vacuum and can occur in dense baryonic matter due to the
explicit violation of Lorentz symmetry are described within a quark model of
the Nambu--Jona-Lasinio type. The temperature and chemical potential dependence
of these processes is investigated. It is found that their contribution to the
production of photons and leptons in heavy-ion collisions is enhanced near the
conditions corresponding to the restoration of chiral symmetry. Moreover, in
the case of the a_0 meson and especially the \rho-meson, a resonant behaviour
(an additional amplification) is observed due to the degeneration of \rho and
a_0 masses when a hot hadron matter is approaching a chirally symmetric phase.Comment: 20 figures, IOP styl
Spectroscopy of resonance decays in high-energy heavy-ion collisions
Invariant mass distributions of the hadronic decay products from resonances
formed in relativistic heavy ion collision (RHIC) experiments are investigated
with a view to disentangle the effects of thermal motion and the phase space of
decay products from those of intrinsic changes in the structure of resonances
at the freeze-out conditions. Analytic results of peak mass shifts for the
cases of both equal and unequal mass decay products are derived. The shift is
expressed in terms of the peak mass and width of the vacuum or medium-modified
spectral functions and temperature. Examples of expected shifts in meson (e.g.,
rho, omega, and sigma) and baryon (e.g., Delta) resonances that are helpful to
interpret recent RHIC measurements at BNL are provided. Although significant
downward mass shifts are caused by widened widths of the meson in
medium, a downward shift of at least 50 MeV in its intrinsic mass is required
to account for the reported downward shift of 60-70 MeV in the peak of the
rho-invariant mass distribution. An observed downward shift from the vacuum
peak value of the Delta distinctively signals a significant downward shift in
its intrinsic peak mass, since unlike for the rho-meson, phase space functions
produce an upward shift for the Delta isobar.Comment: published version with slight change of title and some typos
corrected, 12 pages, 5 figure
Hadro-Chemistry and Evolution of (Anti-) Baryon Densities at RHIC
The consequences of hadro-chemical freezeout for the subsequent hadron gas
evolution in central heavy-ion collisions at RHIC and LHC energies are
discussed with special emphasis on effects due to antibaryons. Contrary to
naive expectations, their individual conservation, as implied by experimental
data, has significant impact on the chemical off-equilibrium composition of
hadronic matter at collider energies. This may reflect on a variety of
observables including source sizes and dilepton spectra.Comment: 4 pages ReVTeX incl. 3 ps-figs, submitted to PR
- …