During the 1996 lead run time, CERES has accumulated 42 million events, corresponding to a factor of 5 more statistics than in 1995 and 2.5 million events of a special photon-run. We report on the ...results of the low-mass e
+e
−-pair analysis. Since the most critical item is the poor signal-to-background ratio we also discuss the understanding of this background, in absolute terms, with the help of a detailed Monte Carlo simulation. We show preliminary results of the photon analysis and summarize the results of the hadron analysis preliminarily reported on already at QM'97 1.
It is shown that the Fisher droplet model, percolation, and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling ...(one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors show a power-law dependence on cluster size with an exponent of 0.42+/-0.02. The EOS Collaboration Au multifragmentation data yield barriers with a power-law exponent of 0.68+/-0.03. Values of the surface energy coefficient of a low density nuclear system are also extracted.
Differential triangular flow, v3(pT), of negative pions is measured at sNN=17.3 GeV around midrapidity by the CERES/NA45 experiment at CERN in central PbAu collisions in the range 0–30% with a mean ...centrality of 5.5%. This is the first measurement as a function of transverse momentum of the triangular flow at SPS energies. The pT range extends from about 0.05 GeV/c to more than 2 GeV/c. The triangular flow magnitude, corrected for the HBT effects, is smaller by a factor of about 2 than the one measured by the PHENIX experiment at RHIC and the ALICE experiment at the LHC. Within the analyzed range of central collisions no significant centrality dependence is observed. The data are found to be well described by a viscous hydrodynamic calculation combined with an UrQMD cascade model for the late stages.
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/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with \(N_{\rm ch}\), and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at \(m\approx\) 500 MeV/c2, 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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