114 research outputs found
Thermal Dileptons as Fireball Thermometer and Chronometer
Thermal dilepton radiation from the hot fireballs created in high-energy
heavy-ion collisions provides unique insights into the properties of the
produced medium. We first show how the predictions of hadronic many-body theory
for a melting meson, coupled with QGP emission utilizing a modern
lattice-QCD based equation of state, yield a quantitative description of
dilepton spectra in heavy-ion collisions at the SPS and the RHIC beam energy
scan program. We utilize these results to systematically extract the excess
yields and their invariant-mass spectral slopes to predict the excitation
function of fireball lifetimes and (early) temperatures, respectively. We
thereby demonstrate that future measurements of these quantities can yield
unprecedented information on basic fireball properties. Specifically, our
predictions quantify the relation between the measured and maximal fireball
temperatures, and the proportionality of excess yields and total lifetime. This
information can serve as a "caloric" curve to search for a first-order QCD
phase transition, and to detect non-monotonous lifetime variations possibly
related to critical phenomena.Comment: 4 pages 3 figure
Finite pion width effects on the rho-meson and di-lepton spectra
Within a field theoretical model where all damping width effects are treated
self-consistently we study the changes of the spectral properties of rho-mesons
due to the finite damping width of the pions in dense hadronic matter at finite
temperature. The corresponding effects in the di-lepton yields are presented.
Some problems concerning the self consistent treatment of vector or gauge
bosons are discussed.Comment: Invited talk given at International Workshop "Gross properties of
Nuclei and Nuclear Exitations", Hirschegg, Austria, 16-22.01.2000, Latex, 7
page
Comprehensive Interpretation of Thermal Dileptons at the SPS
Employing thermal dilepton rates based on medium-modified electromagnetic
correlation functions we show that recent dimuon spectra of the NA60
collaboration in central In-In collisions at the CERN-SPS can be understood in
terms of radiation from a hot and dense hadronic medium. Earlier calculated
\rho-meson spectral functions, as following from hadronic many-body theory,
provide an accurate description of the data up to dimuon invariant masses of
about M\simeq 0.9 GeV, with good sensitivity to details of the predicted
\rho-meson line shape. This, in particular, identifies baryon-induced effects
as the prevalent ones. We show that a reliable description of the \rho
contribution opens the possibility to study further medium effects: at higher
masses (M \simeq 0.9-1.5 GeV) 4-pion type annihilation is required to account
for the experimentally observed excess indicating precursor effects of chiral
symmetry restoration (``chiral mixing''), while remaining structures in the
\omega and \phi region are suggestive for modifications in their line shapes as
well.Comment: 4 pages, 4 figures, v2: slightly improved estimate of four-pion
contributions; accepted for publication in Phys. Rev. Let
Melting rho Meson and Thermal Dileptons
We give a brief survey of theoretical evaluations of light vector mesons in
hadronic matter, focusing on results from hadronic many-body theory. We
emphasize the importance of imposing model constraints in obtaining reliable
results for the in-medium spectral densities. The latter are subsequently
applied to the calculation of dilepton spectra in high-energy heavy-ion
collisions, with comparisons to recent NA60 data at the CERN-SPS. We discuss
aspects of space-time evolution models and the decomposition of the excess
spectra into different emission sources.Comment: 3 pages, 4 figures, talk at ISMD06, Paraty, Brazil, 2-9 Sep 2006, to
be published in Brazil. Jour. Phy
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