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

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...

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Hauptverfasser: Agakichiev, G, Appelshauser, H, Bielcikova, J, Baur, R, Braun-Munzinger, P, Cherlin, A, Damjanovic, S, Drees, A, Esumi, S, Faschingbauer, U, Fraenkel, Z, Fuchs, Ch, Gatti, E, Glassel, P, Hering, G, Heros, C. P. de los, Holl, P, Jung, Ch, Lenkeit, B, Marin, A, Messer, F, Messer, M, Miskowiec, D, Nix, O, Panebrattsev, Yu, Pfeiffer, A, Rak, J, Ravinovich, I, Razin, S, Rehak, P, RIchter, M, Sampietro, M, Sako, H, Saveljic, N, Schmitz, W, Schukraft, J, Seipp, W, Shimanskiy, S, Socol, E, Specht, H. J, Stachel, J, Tel-Zur, G, Tserruya, I, Ullrich, T, Voigt, C, Voloshin, S, Weber, C, Wessels, J. P, Wienold, T, Wurm, J. P, Yurevich, V
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Zusammenfassung: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.
DOI:10.48550/arxiv.nucl-ex/0506002