We present results of a two-pion correlation analysis performed with the Au+Pb collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the ...reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the AGS and at RHIC.
Eur.Phys.J.C41:475-513,2005 We present the combined results on electron-pair production in 158 GeV/n
{Pb-Au} ($\sqrt{s}$= 17.2 GeV) collisions taken at the CERN SPS in 1995 and
1996, and give a ...detailed account of the data analysis. The enhancement over
the reference of neutral meson decays amounts to a factor of 2.31$\pm0.19
(stat.)\pm0.55 (syst.)\pm0.69 (decays)$ for semi-central collisions (28%
$\sigma/\sigma_{geo}$) when yields are integrated over $m>$ 200 MeV/$c^2$ in
invariant mass. The measured yield, its stronger-than-linear scaling with
$N_{ch}$, and the dominance of low pair $p_t$ strongly suggest an
interpretation as {\it thermal radiation} from pion annihilation in the
hadronic fireball. The shape of the excess centring at $m\approx$ 500
MeV/$c^2$, however, cannot be described without strong medium modifications of
the $\rho$ meson. The results are put into perspective by comparison to
predictions from Brown-Rho scaling governed by chiral symmetry restoration, and
from the spectral-function many-body treatment in which the approach to the
phase boundary is less explicit.
We present the combined results on electron-pair production in 158 GeV/n {Pb-Au} (\(\sqrt{s}\)= 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data ...analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31\(\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays)\) for semi-central collisions (28% \(\sigma/\sigma_{geo}\)) when yields are integrated over \(m>\) 200 MeV/\(c^2\) in invariant mass. The measured yield, its stronger-than-linear scaling with \(N_{ch}\), and the dominance of low pair \(p_t\) strongly suggest an interpretation as {\it thermal radiation} from pion annihilation in the hadronic fireball. The shape of the excess centring at \(m\approx\) 500 MeV/\(c^2\), however, cannot be described without strong medium modifications of the \(\rho\) meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.
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