Dielectron Production in Heavy Ion Collisions at 158 GeV/c per Nucleon

TL;DR

This study investigates low-mass dielectron production in heavy ion collisions at CERN, confirming an excess over expected meson decay contributions and supporting in-medium modification theories, while also developing new detector mirror technology.

Contribution

The paper provides a detailed re-analysis of dielectron data, confirms excess production, and introduces a novel lightweight mirror technology for improved detector performance.

Findings

Dielectron production is enhanced by a factor of 3 over expectations.

Data favors models including in-medium effects.

Development of ultralightweight mirrors for RICH detectors.

Abstract

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 dielectron production in the mass range of 0.25<m(ee)<2GeV/c**2 is enhanced by a factor of 3.0+-1.3(stat.)+-1.2(syst.) over the expectation from neutral meson decays. The data is compared to transport model calculations and seem to favor the version including in-medium effects. Furthermore, the development of a new technology to manufacture ultralightweight mirrors for Ring Imaging Cherenkov detectors (RICH) is described. Replacement of the RICH-2 glass mirror by a mirror almost transparent to electrons would considerably improve the performance of the upgraded CERES detector system including a radial Time Projection Chamber (TPC).