The exclusive photoproduction of e+e− pairs from nucleons close to the
vector meson production threshold (1.4<s<1.8 GeV) results from two
main processes: the emission of Bethe-Heitler pairs and the photoproduction of
ρ0- and ω-mesons decaying into e+e− pairs. The Bethe-Heitler
amplitudes are purely electromagnetic and reflect mostly the nucleon magnetic
structure. The γN→e+e−N amplitudes arising from vector meson
production and decay are derived from γN→ρ0N and γN→ωN amplitudes supplemented by the Vector Meson Dominance assumption. The
vector meson photoproduction amplitudes are calculated using a relativistic and
unitary coupled-channel approach to meson-nucleon scattering. They depend
sensitively on the coupling of vector fields to baryon resonances. The γN→e+e−N differential cross sections display interference patterns. The
interference of Bethe-Heitler pair production with vector meson e+e− decay
is quite small in the domain of validity of our model for all angles of the
emitted e+e− pair. The interference of ρ0- and ω-mesons in the
e+e− channel can be large. It is constructive for the γp→e+e−p reaction and destructive for the γn→e+e−n reaction. We
discuss the shape and magnitude of the e+e− pair spectra produced in the
γp→e+e−p and γn→e+e−n reactions as functions of
the pair emission angle and of the total center of mass energy s.Comment: 28 pages, 12 figure