  The $\rho^0-\omega$ interference has been studied in the dilepton invariant
mass distribution spectra in the photonuclear reaction, but that is not done
for the gamma-nucleon reaction. Recent past, the $e^+e^-$ invariant mass
distribution 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 is
calculated 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 is
described by the Vector Meson Dominance (VMD) model which consists of diagonal
and off-diagonal processes. The diagonal process is described as $\gamma \to V;
~Vp \to Vp$. The low energy $\omega$ meson photoproduction data is well
described by the off-diagonal process which is illustrated as $\gamma \to
\rho^0; ~\rho^0 p \to \omega p$. The reaction $\rho^0p \to \omega p$ proceeds
due 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 are
compared, and the significance of the pion exchange interaction is investigated
in the energy region of $\gamma$ beam available at Jefferson Laboratory.
