Search

Within QCD sum rules at finite baryon density we show the crucial role of four-quark condensates, such as ‹(overline{q} γμλaq)2›n, for the in-medium modification of the ωmeson spectral function. In particular, such a global property as the sign of the in-medium omega meson mass shift is found to be governed by a parameter which describes the strength of the density dependence of the four-quark condensate beyond mean-field approximation. To study self-consistently the broadening of the omega meson resonance we employ a hadron spectral function based on the omega meson propagator delivered by a effective chiral Lagrangian. Measurements of the ωmeson spectral change in heavy-ion collisions with the HADES detector can reveal the yet unknown density dependence of the four-quark condensate.

The dependence of the radiative energy loss of hard partons (E

QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of pole mass parameters for the lightest vector mesons $\rho$, $\omega$ and $\phi$ in a strongly interacting medium at conditions relevant for the starting experiments at HADES. The role of the four-quark condensate is highlighted. A few estimates (within a fire ball model and BUU calculations) of dilepton spectra in heavy-ion collisions at 1 AGeV are presented., Comment: contribution to the XL International Winter Meeting on Nuclear Physics, Bormio (Italy), January 20 - 26, 2002

A unique parameterization of secondary dilepton yields in heavy-ion experiments at CERN-SPS is proposed. This parameterization resembles a thermal q \bar q annihilation rate and is supported by the ''dual'' description of hot, strongly interacting matter within either a hadronic or partonic base. Adding the thermal yield and the background contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 and HELIOS/3 data in experiments with lead and sulfur beams can be well described.

The dependence of the radiative energy loss of fast partons on the initial thermodynamic parameters is studied for deconfined matter to be expected at RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic dependence of the energy loss on the propagated distance leads to a strong increase of the energy loss with increasing initial entropy of deconfined matter supposed its life-time is less than the average time to pass through the medium. This is in contrast to a parameterization with constant energy loss per unit length of propagation. For a sufficiently high initial temperature a two-regime behavior of the energy loss as a function of the initial parton momentum occurs. The angular structure of the energy loss of hard jets with respect to the initial temperature is also discussed for RHIC conditions., Comment: 10 pages with figs

Extended duality is used to explain the dilepton data of heavy-ion experiments at CERN-SPS. Taking into account the background contributions (hadronic cocktail, Drell-Yan, semileptonic decays of open charm) the spectral shapes of the CERES, NA38/50 and HELIOS-3 data in experiments with lead and sulfur beams can be well described, however, the normalizations of the sulfur beam data are problematic., talk at the International Workshop XXVIII on Gross Properties of Nuclei and Nuclear Excitations, Hirschegg, Jan. 2000

The polarization of a surrounding QCD medium modifies the induced gluon radiation spectrum of a high-energy parton at small transverse momenta for a single interaction and for multiple scatterings as well. This effect is an analogue of the Ter-Mikaelian effect in QED, superimposed to the Landau--Pomeranchuk effect, however it appears in QCD in a different phase space region.

An analysis of the dilepton measurements of the reactions Pb(158 A$\cdot$GeV) + Au, Pb by the CERES and NA50 collaborations points to a unique thermal source contributing to the invariant mass and transverse momentum spectra., 7 LaTeX pages including eps figures

We study the prospects to get information about the early and hot stages of deconfined matter produced in relativistic heavy-ion collisions by analyzing dilepton and single-lepton spectra. Energy losses of heavy quarks in deconfined matter and thermalization effects in hadron matter and their influence on lepton spectra are considered., 8 LaTeX pages including eps figures, contribution to the 37th International Winter Meeting on Nuclear Physics, Bormio, Jan 25-29, 1999

In ultrarelativistic heavy-ion collisions at √s > 20 (120) A GeV a copious production of charm (bottom) production sets in which, via correlated semileptonic DD (BB) decays, gives rise to a dilepton yield at invariant mass M ≈ 2 - 3 GeV in excess of the Drell-Yan yield and the thermal dilepton signal from deconfined matter as well. We show that appropriate single-electron transverse momentum cuts (suitable for ALICE at LHC) cause a threshold like behavior of the dilepton spectra from heavy-quark meson decays and the Drell-Yan process and can allow to observe a thermal dilepton signal from hot deconfined matter.

The spectra of lepton pairs from correlated open charm and bottom decays in ultrarelativistic heavy-ion collisions are calculated. Our approach includes energy loss effects of the fast heavy quarks in deconfined matter which are determined by temperature and density of the expanding parton medium. We find a noticeable suppression of the initial transverse momentum spectrum of heavy quarks due to the energy loss within the central rapidity covered by the PHENIX detector system. As a result the dilepton yields from correlated decays of heavy quarks are in the same order of magnitude as the Drell-Yan signal., Comment: Contribution to the Proceedings of ''RHIC'97 Summer Study'' July 7 - 16, 1997, Brookhaven National Lab

The spectra of lepton pairs from correlated open charm and bottom decays in ultrarelativistic heavy-ion collisions are calculated. Our approach includes energy loss effects of the fast heavy quarks in deconfined matter which are determined by temperature and density of the expanding parton medium. We find a strong suppression of the initial transverse momentum spectrum of heavy quarks due to the energy lass at LHC conditions. Within the central rapidity covered by the ALICE detector system, the dominant contribution from bottom decays to the high invariant mass dielectron spectrum is predicted.

The hard initial production of open charm and dileptons is compared with possible thermal signals in heavy-ion collisions at RHIC and LHC energies. Our approach is based on the perturbative QCD mini-jet mechanism of quark-gluon matter formation. The thermal dilepton signal is found to rise much stronger as compared to the hard Drell - Yan background with increasing collider energy and clearly dominates at LHC energy. Oppositely, open charm stems from initial hard production. A possible rnanifestation of gluon shadowing at RHIC and LHC energies is discussed.