Using the high energy color dipole approach, we study the exclusive photoproduction of lepton pairs $\gamma N\to {\gamma }^{*}(\to {\ell }^{+}{\ell }^{-})N$ (with $N=p$, $A$). We use simple models for the elementary dipole-hadron scattering amplitude that captures main features of the dependence on atomic number $A$, on energy and on momentum transfer $t$. This investigation is complementary to conventional partonic description of timelike Compton scattering, which considers quark handbag diagrams at leading order in ${\alpha }_s$ and simple models of the relevant generalized parton distributions. These calculations are input in electromagnetic interactions in $pp$ and $AA$ collisions to measured at the LHC.

• Received 20 May 2008

DOI:https://doi.org/10.1103/PhysRevD.78.034016