Quantum interferences in the image reaction close to the vector meson production threshold Original Research Article

The exclusive photoproduction of e+e− pairs from nucleons close to the vector meson production threshold (View the MathML source) 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 View the MathML source reaction and destructive for the View the MathML source reaction. We discuss the shape and magnitude of the e+e− pair spectra produced in the View the MathML source and View the MathML source reactions as functions of the pair emission angle and of the total center of mass energy View the MathML source. In the particular kinematics under consideration, our results suggest that the vector meson contribution can be determined quite accurately from experimental e+e− spectra by subtracting the Bethe–Heitler term and neglecting the small interference of Bethe–Heitler pairs with vector meson e+e− decays.