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The $\rho^0-\omega$ interference has been studied in the dilepton invariantmass distribution spectra in the photonuclear reaction, but that is not donefor the gamma-nucleon reaction. Recent past, the $e^+e^-$ invariant massdistribution spectrum in the $\gamma p$ reaction, i.e., $\gamma p \to pe^+e^-$reaction, was measured at Jefferson Laboratory to look for the $\rho^0 -\omega$interference in the multi-GeV region. To study the mechanism of this reaction,the differential cross section of the $e^+e^-$ invariant mass distribution iscalculated in the quoted energy region. The reaction is assumed to proceed as$\gamma p \to Vp$; $V \to e^+e^-$, where $V$ denotes a vector meson, i.e.,either $\rho^0$ or $\omega$ meson. The photoproduction of the vector meson isdescribed by the Vector Meson Dominance (VMD) model which consists of diagonaland off-diagonal processes. The diagonal process is described as $\gamma \to V;~Vp \to Vp$. The low energy $\omega$ meson photoproduction data is welldescribed by the off-diagonal process which is illustrated as $\gamma \to\rho^0; ~\rho^0 p \to \omega p$. The reaction $\rho^0p \to \omega p$ proceedsdue to one pion exchange interaction. The differential cross sections of the$\gamma p \to pe^+e^-$ reaction due to the above processes of VMD model arecompared, and the significance of the pion exchange interaction is investigatedin the energy region of $\gamma$ beam available at Jefferson Laboratory.

Pion exchange interaction in the $\gamma p \to p e^+e^-$ reaction