122683216
Resonance Multiplicities in a Hadron Transport Approach
In this article we focus on the multiplicities of resonances, ratios of resonant over non-resonant states and rescattering processes in heavy ion collisions. Therefore we utilize a hadron transport model (UrQMD vl.3). We find that rescattering of decay particles is of great importance when studying resonances in a hadronic medium.
117905049
How can we explore the onset of deconfinement by experiment
There is little doubt that Quantumchromodynamics (QCD) is the theory which describes strong interaction physics. Lattice gauge simulations of QCD predict that in the $\mu,T$ plane there is a line where a transition from confined hadronic matter to deconfined quarks takes place. The transition is either a cross over (at low $\mu$) or of first order (at high $\mu$). It is the goal of the present and future heavy ion experiment at RHIC and FAIR to study this phase transition at different locations in the $\mu,T$ plane and to explore the properties of the deconfined phase. It is the purpose of this contribution to discuss some of the observables which are considered as useful for this purpose.
118400528
Evidence for the a(1) meson being a difficult messenger for the restoration of chiral symmetry
We perform a theoretical analysis of the ${a}_{1}$ resonance mass spectrum in ultrarelativistic heavy ion collisions within a hadron/string transport approach. Predictions for the ${a}_{1}$ yield and its mass distribution are given for the GSI-FAIR and the critRHIC energy regime. The potential of the ${a}_{1}$ meson as a signal for chiral symmetry restoration is explored. In view of the latest discussion, we investigate the decay channel ${a}_{1}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\pi}$ in detail and find a strong bias toward low ${a}_{1}$ masses. This apparent mass shift of the ${a}_{1}$, if observed in the $\ensuremath{\gamma}\ensuremath{\pi}$ channel, might render a possible mass shift due to chiral symmetry restoration very difficult to disentangle from the decay kinematics.
117180320
Dynamic canonical suppression of strangeness in transport models
It is investigated whether canonical suppression associated with the exact conservation of an U(1)-charge can be reproduced correctly by current transport models. Therefore a pion-gas having a volume-limited cross section for kaon production and annihilation is simulated within two different transport prescriptions for realizing the inelastic collisions. It is found that both models can indeed dynamically account for the canonical suppression in the yields of rare strange particles.
16622057
The influence of bulk evolution models on heavy-quark phenomenology
We study the impact of different Quark-Gluon Plasma expansion scenarios in heavy-ion collisions on spectra and elliptic flow of heavy quarks. For identical heavy-quark transport coefficients relativistic Langevin simulations with different expansion scenarios can lead to appreciable variations in the calculated suppression and elliptic flow of the heavy-quark spectra, by up to a factor of two. A cross comparison with two sets of transport coefficients supports these findings, illustrating the importance of realistic expansion models for quantitative evaluations of heavy-quark observables in heavy-ion collisions. It also turns out that differences in freeze-out prescriptions and Langevin realizations play a significant role in these variations. Light-quark observables are essential in reducing the uncertainties associated with the bulk-matter evolution, even though uncertainties due to the freeze-out prescription persist.
17609019
How sensitive are di-leptons from rho mesons to the high baryon density region?
We show that the measurement of dileptons might provide only a restricted view into the most dense stages of heavy-ion reactions. Thus, possible studies of meson and baryon properties at high baryon densities, as, e.g., done at the GSI High Acceptance DiElectron Spectrometer (HADES) and envisioned for the Facility for Antiproton and Ion Research (FAIR) compressed baryonic matter experiments, might observe weaker effects than currently expected in certain approaches. We argue that the strong absorption of resonances in the high-baryon-density region of the heavy-ion collision masks information from the early hot and dense phase due to a strong increase of the total decay width because of collisional broadening. To obtain additional information, we also compare the currently used approaches to extract dileptons from transport simulations, i.e., shining, only vector mesons from final baryon resonance decays and instant emission of dileptons and find a strong sensitivity on the method employed in particular at FAIR and the CERN Super Proton Synchrotron energies. It is shown explicitly that a restriction to \ensuremath{\rho} meson (and therefore dilepton) production only in final-state baryon resonance decays provide a strong bias toward rather low baryon densities. The results presented are obtained from ultrarelativistic quantum molecular dynamics v2.3 calculations using the standard setup.
2297347
Radio Observations of AGN in Low Surface Brightness Galaxies
We present preliminary results of a study of the low frequency radio continuum emission from the nuclei of Giant Low Surface Brightness (LSB) galaxies. We have mapped the emission and searched for extended features such as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star formation and generally less evolved compared to nearby bright spirals. This paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz, 610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations were done with the GMRT. Radio cores as well as extended structures were detected and mapped in all three galaxies; the extended emission may be assocated with jets/lobes associated with AGN activity. Our results indicate that although these galaxies are optically dim, their nuclei can host AGN that are bright in the radio domain.