437 research outputs found
Probing meson spectral functions with double differential dilepton spectra in heavy-ion collisions
The double differential dilepton spectrum at fixed
transverse mass allows a direct access to the vector meson spectral
functions. Within a fireball model the sensitivity of
against variations of both the in-medium properties of mesons and the dynamics
of the fireball is investigated. In contrast to the integrated invariant-mass
spectrum , in the spectrum with fixed
the signal is clearly seen as bump riding on the background
even in case of strong in-medium modifications.Comment: 11 pages with figs. (style changed to RevTeX
Jet-induced gauge field instabilities in the quark-gluon plasma: A kinetic theory approach
We discuss the properties of the collective modes of a system composed by a
thermalized quark-gluon plasma traversed by a relativistic jet of partons. The
transport equations obeyed by the components of the plasma and of the jet are
studied in the Vlasov approximation. Assuming that the partons in the jet can
be described with a tsunami-like distribution function we derive the
expressions of the dispersion law of the collective modes. Then the behavior of
the unstable gauge modes of the system is analyzed for various values of the
velocity of the jet, of the momentum of the collective modes and of the angle
between these two quantities. We find that the most unstable modes are those
with momentum orthogonal to the velocity of the jet and that these
instabilities appear when the velocity of the jet is higher than a threshold
value, which depends on the plasma and jet frequencies. The results obtained
within the Vlasov approximation are compared with the corresponding results
obtained using a chromohydrodynamical approach.The effect we discuss here
suggests a possible collective mechanism for the description of the jet
quenching phenomena in heavy ion collisions.Comment: 13 pages, 6 figure
Confinement in the Big Bang and Deconfinement in the Little Bangs at CERN-SPS
The evolution of strongly interacting matter during the cosmological
confinement transition is reviewed. Despite of many proposed relics no specific
signal from the rearrangement of quarks and gluons into hadrons has been
identified by observations. In contrast to this, several observables in
heavy-ion collisions at CERN-SPS energies point to the creation of a matter
state near or slightly above deconfinement. We focus here on the analysis of
dileptons and direct photons. Similarities and differences of the Big Bang and
the Little Bang confinement dynamics are elaborated.Comment: 8 pages, invited talk at Luederitz 2000, "Fundamental and Applied
Aspects of Modern Physics", Nov. 13 - 17, 200
Probing in-medium vector meson decays by double-differential di-electron spectra in heavy-ion collisions at SIS energies
Within a transport code simulation for heavy-ion collisions at bombarding
energies around 1 AGeV, we demonstrate that double-differential di-electron
spectra with suitable kinematical cuts are useful to isolate (i) the
meson peak even in case of strong broadening, and (ii) the in-medium
decay contribution. The expected in-medium modifications of the vector meson
spectral densities can thus be probed in this energy range via the di-electron
channel
Evaluation of QCD sum rules for light vector mesons at finite density and temperature
QCD sum rules are evaluated at finite nucleon densities and temperatures to
determine the change of mass parameters for the lightest vector mesons ,
and in a strongly interacting medium. For conditions relevant
for the starting experiments at HADES we find that the in-medium mass shifts of
the and mesons are governed, within the Borel QCD sum rule
approach, by the density and temperature dependence of the four-quark
condensate. In particular, the variation of the strength of the density
dependence of the four-quark condensate reflects directly the decreasing mass
of the meson and can lead to a change of the sign of the meson
mass shift as a function of the density. In contrast, the in-medium mass of the
meson is directly related to the chiral strange quark condensate which
seems correspondingly accessible
Probing the strange quark condensate by di-electrons from phi meson decays in heavy-ion collisions at SIS energies
QCD sum rules predict that the change of the strange quark condensate in hadron matter at finite baryon density causes a shift of the peak
position of the di-electron spectra from meson decays. Due to the
expansion of hadron matter in heavy-ion collisions, the peak suffers a
smearing governed by the interval of density in the expanding fireball, which
appears as effective broadening of the di-electron spectrum in the
region. The emerging broadening is sensitive to the in-medium change of . This allows to probe directly in-medium modifications of
via di-electron spectra in heavy-ion collisions at SIS energies with HADES
A unique large thermal source of real and virtual photons in the reactions Pb(158 AGeV) + Pb, Au
The data of direct single-photon measurements of the WA98 collaboration in
the reaction Pb(158 AGeV) + Pb are analyzed within a thermal model with a
minimum number of parameters adjusted to the dilepton data obtained by the
CERES and NA50 collaborations in the reactions Pb(158 AGeV) + Au, Pb. The
agreement of our model with the WA98 data points to a unique large thermal
source emitting electromagnetic radiation observable in both the real and
virtual photon channels.Comment: 11 pages including figure
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