204 research outputs found
In-Medium Vector Mesons, Dileptons and Chiral Restoration
Medium modifications of the electromagnetic spectral function in hadronic and
quark-gluon matter are reviewed. A strong broadening of the meson, which
dominates the spectral function in the low-mass regime, is quantitatively
consistent with dilepton excess spectra measured in photoproduction off cold
nuclei (CLAS/JLab) and in fixed-target ultrarelativistic heavy-ion collisions
(NA45,NA60/CERN-SPS). The large excess observed by PHENIX at RHIC remains
unexplained to date, but is most likely not due to emission from the
Quark-Gluon Plasma. Connections to thermal lattice QCD promise progress in the
search for chiral symmetry restoration.Comment: 9 pages, 12 figures, Proceedings of Chiral 2010 (Valencia, June
21-24, 2010
Intermediate-Mass Dileptons at the CERN-SpS and RHIC
The significance of thermal dilepton radiation at intermediate invariant
masses (1GeV<M<3GeV) in ultrarelativistic heavy-ion collisions is investigated.
At CERN-SpS energies, a consistent explanation of the excess observed by NA50
can be given. At RHIC energies the thermal signal is dominated by early
emission indicative for QGP formation. Chemical under-saturation effects and
the competition with open-charm contributions are addressed.Comment: Invited talk at the International Workshop XXVIII on Gross Properties
of Nuclei and Nuclear Excitations, 'Hadrons in Dense Matter', Hirschegg
(Austria), Jan. 16-22, 2000; 8 pages LaTeX including 11 eps/ps-figure
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
Production of Light Nuclei at Thermal Freezeout in Heavy-Ion Collisions
We revisit the problem of the production of light atomic nuclei in
ultrarelativistic heavy-ion collisions. While their production systematics is
well produced by hadro-chemical freezeout at temperatures near the QCD
pseudo-critical temperature, their small binding energies of a few MeV per
nucleon suggest that they cannot survive as bound states under these
conditions. Here, we adopt the concept of effective chemical potentials in the
hadronic evolution from chemical to thermal freezeout (at typically 100\,MeV), which, despite frequent elastic rescatterings in
hadronic matter, conserves the effective numbers of particles which are stable
under strong interactions, most notably pions, kaons and nucleons. It turns out
that the large chemical potentials that build up for antibaryons result in
thermal abundances of light nuclei and antinuclei, formed at thermal freezeout,
which essentially agree with the ones evaluated at chemical freezeout. Together
with their transverse-momentum spectra, which also indicate a kinetic freezeout
near , this provides a natural explanation for their production
systematics without postulating their survival at high temperatures.Comment: 5 pages, 7 figures, v2: "Note added" correcte
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