Electron-positron pairs as a probe for hadrons in dense matter
Gesellschaft für Schwerionenforschung, Planckstr. 1, D-64291, Darmstadt, Germany
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In this paper the latest results from the analysis of e + e --pairs emitted in Pb + Au collisions at 40 AGeV/c and a combined analysis of all data available at 158 AGeV/c are presented. The enhancement of low-mass e + e --pairs (m ee > 0.2 GeV/c 2) with respect to the expected yield from hadron decays first reported at 158 AGeV/c is also found at 40 AGeV/c and is even larger there. Comparing to various theoretical models based on annihilation, the data can only be reproduced, if the properties of the intermediate in the hot and dense medium are modified. Hadron data taken at the same beam energies sheds light on the dynamical evolution of the fireball and addresses the question whether the medium modification is linked to baryon density rather than temperature. In the future e + e --pairs emitted in heavy-ion collisions will be measured at the LHC with the ALICE Transition Radiation Detector (TRD). Here, special emphasis will be put on the production of heavy vector mesons (, ).
© Società Italiana di Fisica and Springer-Verlag, 2003