Dielectron production in heavy ion collisions at 158 GeV/c per nucleon

In this paper, the low-mass electron pair production in 158 AGeV/c Pb - Au collisions is investigated with the Cherenkov Ring Electron Spectrometer (CERES) at the Super Proton Synchrotron accelerator (SPS) at CERN. The main goal is to search for modifications of hadron properties in hot and dense nuclear matter. The presented re-analysis of the 1996 data set is focused on a detailed study of the combinatorial-background subtraction by means of the mixed-event technique. The results confirm previous findings of CERES. The di-electron production in the mass range of $0.25<m_{ee}