Probing the Rho Spectral Function in Hot and Dense Nuclear Matter by Dileptons

Abstract

We present a dynamical study of $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ production in proton-nucleus and nucleus-nucleus collisions at CERN-SPS energies on the basis of the covariant transport approach HSD employing a momentum-dependent $\rho$-meson spectral function that includes the pion modifications in the nuclear medium as well as the polarization of the $\rho$-meson due to resonant $\rho$$-N$ scattering. We find that the experimental data from the CERES and HELIOS-3 Collaborations can be described equally well as within the dropping $\rho$-mass scenario. Whereas corresponding dilepton $q_T$-spectra are found to be very similar, the inclusive dilepton yield in the invariant mass range $0.85\le M\le 1.0$ GeV should allow to disentangle the two scenarios experimentally.

Comments: 13 pages RevTeX slightly revised, 6 eps-figures