Medium Effects in rho-Meson Photoproduction
  We compute dilepton invariant mass spectra from the decays of rho mesons produced by photon reactions off nuclei. Our calculations employ a realistic model for the rho photoproduction amplitude on the nucleon which provides fair agreement with measured cross sections. Medium effects are implemented via an earlier constructed rho propagator based on hadronic many-body theory. At incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB, the average density probed for iron targets is estimated at about half saturation density. At the pertinent rho-meson 3-momenta the predicted medium effects on the rho propagator are rather moderate. The resulting dilepton spectra approximately agree with recent CLAS data. 
F. Riek (1), R. Rapp (1), T.-S. H. Lee (2), Yongseok Oh (1) ((1) Texas   A-M Univ., (2) Argonne Nat. Lab.)