Dilepton Production and M T -scaling at Bevalac/sis Energies *

We present a dynamical study of e + e − production in C + C and Ca + Ca collisions at BEVALAC/SIS energies on the basis of the covariant transport approach HSD employing momentum-dependent ρ-meson spectral functions that include the pion modifications in the nuclear medium as well as the polarization of the ρ-meson due to resonant ρ−N scattering. We find that the experimental data from the DLS collaboration cannot be described within the ρ-meson spectral function approach. A dropping η-mass scenario leads to a good reproduction of the DLS dilepton data, however, violates the m T-scaling of π 0 and η spectra as observed by the TAPS collaboration.