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.

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

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 $\omega$ and $\phi$ 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 $J^P=1^-$ 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 ($\rho, \omega, \phi$) and heavy ($\Psi, \Upsilon$) 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 $\rho-$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