Can one directly test the scalar-vector Lorentz structure of the nucleon- and antinucleon-nucleus potential?

Quantum hadrodynamics in mean-field approximation describes the effective n ucleon-nucleus potential (about -50 MeV deep) as resulting from a strong re pulsive vector (about 400 MeV) and a strong attractive scalar (about -450 M eV) contribution. This scalar-vector Lorentz structure implies a significan t lowering of the threshold for p (p) over bar photoproduction on a nucleus by about 850 MeV as compared with the free case since charge conjugation r everses the sign of the vector potential contribution in the equation of mo tion for the (p) over bar states. We discuss the possibility of measurable signatures of the scalar-vector structure of The nucleon-nucleus potential for the p (p) over bar photoproduction. The p<(p$)over bar> photoproduction cross section is calculated for the target nucleus Pb-208 near threshold. We indicate the increased cross section for emission of charged pions as a consequence of the subsequent (p) over bar annihilation within the nucleus. The inclusive cross section for gamma-induced (p) over bar p creation and the resulting increase of charged pion production are probably too small as compared with the expected background to be measurable.