Analysis of the dilepton invariant mass spectrum in C + C collisions at2Aand1AGeV

Abstract

Recently the HADES Collaboration has published the invariant mass spectrum of ${e}^{+}{e}^{\ensuremath{-}}$ pairs, $\mathit{dN}/{\mathit{dM}}_{{e}^{+}{e}^{\ensuremath{-}}}$, produced in C + C collisions at 2$A$ GeV. Using electromagnetic probes, one hopes to get information from this experiment on hadron properties at high density and temperature. Simulations show that firm conclusions on possible in-medium modifications of meson properties will only be possible when the elementary meson production cross sections, especially in the $\mathrm{pn}$ channel, as well as production cross sections of baryonic resonances are better known. Presently one can conclude that (i) simulations overpredict by far the cross section at ${M}_{{e}^{+}{e}^{\ensuremath{-}}}\ensuremath{\approx}{M}_{\ensuremath{\omega}}^{0}$ if free production cross sections are used and that (ii) the upper limit of the \ensuremath{\eta} decay into ${e}^{+}{e}^{\ensuremath{-}}$ is smaller than the present upper limit of the Particle Data Group. This is the result of simulations using the isospin quantum molecular dynamics approach.