Dilepton Production at SPS Energies

Abstract

We present a nonperturbative dynamical study of $e^{+}{e}^{-}$ production in proton- nucleus and nucleus-nucleus collisions at SPS energies on the basis of a covariant transport approach. For p + A reactions the dilepton yield for invariant masses m $\le$ 1.2 GeV is found to be dominated by the decays of the $\eta ,\rho ,\omega$ and $\Phi$ mesons in line with the findings of the CERES collaboration. For S + Au collisions at 200 GeV/A the dilepton yield is, however, dominated by ${\pi }^{+}{\pi }^{-}$ annihilation due to the high pion densities achieved. Whereas for `free' meson masses and form factors the experimental cross section is slightly underestimated for 0.3 GeV $\le$ m $\le$ 0.45 GeV, different medium modifications of the $\rho$-meson appear compatible with current CERES data.

Comments: 1 compressed uuencoded postscript file with 6 figures included, 18 pages