e + e--pair production in Pb-Au collisions at 158 GeV per nucleon
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- 作者：D. Adamová ; G. Agakichiev ; H. Appelsh?user ; V. Belaga and P. Braun-Munzinger ; et al.
- 刊名：The European Physical Journal C - Particles and Fields
- 出版年：2005
- 出版时间：June 2005
- 年：2005
- 卷：41
- 期：4
- 页码：475-513
- 全文大小：1,600 KB
- 刊物类别：Physics and Astronomy
- 刊物主题：Physics
Elementary Particles and Quantum Field Theory
Nuclear Physics, Heavy Ions and Hadrons
Physics beyond the Standard Model
Measurement Science and Instrumentation
Astronomy, Astrophysics and Cosmology - 出版者：Springer Berlin / Heidelberg
- ISSN：1434-6052
文摘
We present the combined results on electron-pair production in 158 GeV/n Pb-Au (?s\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 ±0.19 (stat.)±0.55 (syst.)±0.69 (decays)\pm0.19 (stat.)\pm0.55 (syst.)\pm0.69 (decays) for semi-central collisions (28%\% s/sgeo\sigma/\sigma_{geo}) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with NchN_{\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 ?m\approx 500 MeV/c2, however, cannot be described without strong medium modifications of the r\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.