Intermediate-mass dilepton spectra and the role of secondary hadronic processes in heavy-ion collisions

Abstract

We carry out a study of intermediate-mass (between 1 and 2.5 GeV) dilepton spectra from hadronic interactions in heavy-ion collisions. The processes considered are $\pi \pi \to l\bar{l}$, $\pi \rho \to l\bar{l}$, $\pi a_1\to l\bar{l}$, $\pi \omega \to l\bar{l}$, $K\bar{K}\to l\bar{l}$, and $K{\bar{K}}^{\ast }+c.c\to l\bar{l}$. The elementary cross sections for those are obtained from chiral Lagrangians involving pseudoscalar, vector, and axial-vector mesons. The respective electromagnetic form factors are determined by fitting to experimental data for the reverse processes of $e^{+}{e}^{-}\to hadrons$. Based on this input we calculate cross sections and thermal dilepton emission rates and compare our results with those from other approaches. Finally we use these elementary cross sections with a relativistic transport model and calculate dilepton spectra in S+W collisions at SPS energies. The comparison of our results with experimental data from the HELIOS-3 collaboration indicates the importance of the secondary hadronic contributions to the intermediate-mass dilepton spectra.

Comments: 25 pages, including 20 postscript figures