1. e+e--pair production in Pb-Au collisions at 158 GeV per nucleon
- Author
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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., and Yurevich, V.
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Nuclear Experiment - 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$\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays)$ 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., Comment: 39 pages, 40 figures, to appear in Eur.Phys.J.C. (2005)
- Published
- 2005
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