e^+e^- Pair Production from $\gamma$ A Reactions

Abstract

We present a calculation of e^+e^- production in $\gamma A$ reactions at MAMI and TJNAF energies within a semi-classical BUU transport model. Dilepton invariant mass spectra for $\gamma$C, $\gamma$Ca and $\gamma$Pb are calculated at 0.8, 1.5 and 2.2 GeV. We focus on observable effects of medium modifications of the $\rho$ and $\omega$ mesons. The in-medium widths of these mesons are taken into account in a dynamical, consistent way. We discuss the transport theoretical treatment of broad resonances.