e+e--pair production in Pb-Au collisions at 158 GeV per nucleon

Abstract

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$\pm 0.19(stat.)\pm 0.55(syst.)\pm 0.69(decays)$ 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.

39 pages, 40 figures, to appear in Eur.Phys.J.C. (2005)

References in corpus (46)

• Big Bang Nucleosynthesis (in "The Review of Particle Properties" 2004)
• Chemical Equilibration in Pb+Pb Collisions at the SPS
• Thermal and Hadrochemical Equilibration in Nucleus-Nucleus Collisions at the SPS
• Hadronic Production of Thermal Photons
• Rho Meson Propagation and Dilepton Enhancement in Hot Hadronic Matter
• Enhancement of low-mass dileptons in heavy-ion collisions
• Chiral Restoration in Hot and/or Dense Matter
• Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum
• Chemical Freeze-out and the QCD Phase Transition Temperature
• Low-Mass Dileptons at the CERN-SpS: Evidence for Chiral Restoration?
• Hydrodynamical Description of 200 A GeV/c S+Au Collisions: Hadron and Electromagnetic Spectra
• On the Manifestation of Chiral Symmetry in Nuclei and Dense Nuclear Matter
• Medium Modifications of the Rho Meson at CERN/SPS Energies
• The Spectral Function of the Rho Meson in Nuclear Matter
• Dilepton Production at SPS Energies
• Equation of State, Radial Flow and Freeze-out in High Energy Heavy Ion Collisions
• Signatures of Thermal Dilepton Radiation at RHIC
• Enhanced Production of Low-Mass Electron Pairs in 40 AGeV Pb-Au Collisions at the CERN SPS
• P-Wave Polarization of the $\rho$-Meson and the Dilepton Spectrum in Dense Matter
• Thermal Dilepton Radiation at Intermediate Masses at the CERN-SpS
• Universal Pion Freeze-out in Heavy-Ion Collisions
• Vector Manifestation of the Chiral Symmetry
• Light Vector Mesons in Nuclear Matter
• Probing the Rho Spectral Function in Hot and Dense Nuclear Matter by Dileptons
• Dilepton production in proton-nucleus and nucleus-nucleus collisions at SPS energies
• Analysis of the HELIOS-3 ${\mu }^{+}{\mu }^{-}$ Data within a Relativistic Transport Approach
• Rho properties in a hot meson gas
• A Microscopic Calculation of Photoabsorption Cross Sections on Protons and Nuclei
• Recent results from Pb-Au collisions at 158 GeV/c per nucleon obtained with the CERES spectrometer
• Dilepton and Photon Emission Rates from a Hadronic Gas II
• Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
• Towards the Quark-Gluon Plasma
• Phases of QCD, Thermal Quasiparticles and Dilepton Radiation from a Fireball
• Production of Eta-Mesons in 200 AGeV/c S+S and S+Au Reactions
• Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies
• Latest Results from CERES/NA45
• New results from CERES
• Chiral Symmetry Restoration and Parity Mixing
• Thermal effects on dilepton production from $\pi -\pi$ annihilation
• The Pion Decay Constants and the Rho-Meson Mass at Finite Temperature in the Hidden Local Symmetry
• In-medium vector meson properties and low-mass dilepton production from hot hadronic matter
• Thermal Dileptons from a Nonperturbative Quark-Gluon Phase
• Photon and dilepton emission rates from high density quark matter
• Photon Rates for Heavy-Ion Collisions from Hidden Local Symmetry
• The effects of meson mixing on dilepton spectra
• Study of the Finite Density State based on SU(2) Lattice QCD

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